Bicycling a Double Century?

I am planning to ride a double century sometime in mid-September. As you guys can see from my training log, I’ve got no shortage of good solid road miles under my belt, including RAGBRAI last week. Most of thehe double century plans I have found are geared towards starting at the beginning of a season. I’ve already completed two centuries this season, so can anyone suggest a plan which will have me ready by, say September 15?

First off, I have never ridden a double century.
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Comfort
I would try to dial in on comfort as much as I can. I think pain will be the main annoyance you will wrestle with. So try to perfect your fit and riding style.
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Fuel
You should try to experiment and dial in what you will eat on the ride. This might be a maker or breaker of success. Find your liquid fuel, and how much you need to drink, and the timing of it, both for energy and hydration (weather you will be riding in will be important), and then there is the issue of solid foods. You need to have figured out what works for you, and experimented with your nutrition on your long training rides.
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Check these out for ideas about food on bike:
http://www.youtube.com/watch?v=Nwt-DUpKPYA
http://www.youtube.com/watch?v=ZGZUohUwDdI
http://www.youtube.com/watch?v=5UiuqIWGe_s
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Training
I would venture to say that this is mostly about having a real strong base. I think there is no way around that.
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The way I would go about building it is to ride lots of Zone 2 rides (endurance pace), and rest as needed in Zone 1, perhaps doing one tempo ride once a week (if you feel like it) is also a good idea. If the double century is a group ride, it is a good idea even to do the tempo ride as a group training ride with your local cycling club. And then there is the once a week LONG ride to push your boundaries in that area.
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What you seem to be lacking a bit, are some medium distance rides. All this is of course very relative. But I would as a default do medium Zone 2 rides as your bread and butter base building, and rest with Zone 1 rides ( can be short or medium, or some where between ), and then the LONG ride that should be ridden as you plan on riding on your big day. Into the mix you can throw a group tempo ride, if you feel like it helps things.
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So slowly inflate your medium rides, and make the LONG one push your boundaries (no good doing a long ride that wont challenge you). The recovery rides you can ride more as you feel like, the important thing is that you actually rest. To me recovery rides are like plugging a power cord in to my legs and refilling them like batteries.
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So gradually inflate those rides, I think it is best to do this by feel, rather than by strict schedule. But ride every day, unless you are sick. If you don’t feel like riding, just ride very easy and very short, but get on the bike. ;)
(If you are doing some speed work and really drain your self to the bone, then you can take an off day.)
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And don’t forget to eat enough with all this riding. If your legs often feel rather empty, try eating more carbs, even simple carbs, sugary things like cookies, chocolate milk or just what you like. – And yes, drink some big calorie drink after you ride, with a combination of carbs and proteins. I personally use gainer type drinks, that body builders use to bulk up on.
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If you got a foam roller or are so lucky to have some one to massage you, then foam roll or get a massage. More the better. Can have a huge effect on recovery. Yes, and take your Multivitamins&Minerals, and omega 3-6 while you are at it. Only use quality vitamins, the rest are not worth taking.
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Recovery dictates how much you can ultimately train and progress by it. So be mindful of resting and taking care of your legs. Recovery is almost an art. ;)
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Ride lots. ;)

@arnthorla what would you consider a medium distance ride? My morning ride is generally ~20 miles and on weekends i will do 40-60mi Saturday, ~30 Sunday.

That is the thing, it is very relative. ;) It is relative to your form, where you are at in your training. For me it would start at about 70 km – 100 km (43-63 miles) depending on where I am at. And long for me would be around 100 km – 160 km (63-100 miles) depending on where I am in the process. The longest races that I would possibly partake in would be 120 km, so I don’t put great emphasis on going further than that on my long rides. You could go a bit further with this, at least with your weekly long ride. – ( I am at the lower end of the spectrum at the moment, but at the time when I could raise the bar to the other end. Because my medium rides have become about as long as my long ride, so I should be reaching a bit longer with my long ride. But at the moment I am working on my tempo so I have not gone that way, it needs more work for me at the moment. I am more interested in increasing my average speed on lower intensities and perhaps increasing my threshold power (good for time trials and such).) – You should even venture further than this if you feel your body can deal with it. Don’t force it though. You might gently nudge your body, but you must recover, else you are just backsliding. Doing 2 days of recovery riding should be enough to get you fully rested, while in base building if you are feeling more tired than usual, and it is better to under train than to over train, it is much easier to fix. ;) – About recovery riding. You must have the discipline to pace your self to an easy pace. Breathing through your nose most of the time can be a useful gauge. If you are having a difficult time just breathing through your nose on recovery rides, then you might be going to hard, or you need to blow your nose. ;)
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But the the key thing is to build this up gradually. You medium distance should not be hard for you, it should be enough so that you feel that you have done a good ride, but it should not feel hard or real draining.
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Your form should allow you to inflate the medium distance, you should not force it too much. The long ride is a different matter it is about pushing your buttons distance wise. And the short rides should also follow rises in medium distance, but when you are really tired you can of course shorten it. But as I was saying I feel that the middle distance is the center of gravity, and is the real measure of your base.
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As your base comes along you should see your HR drop for the same work rate. You might start with your HR at the top of your zone, and end up having difficulty raising it up into the zone later in your base training. If you have a power meter then you will see the ratio of av.watts/av.HR rise as your base training progresses.
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But #1, listen to your body and don’t worry too much about being overly analytical about your training. But do read up on every thing you can find, and you will find that there are certain basic rules that run through most peoples idea of training and cycling training. So you will kind of feel that you could go further with your medium rides when you can, and then you should. And you could do it by increasing the distance for one or two medium rides in a sort of transition week.
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One thing that can also work, in planning your training. Is to think in blocks, not weeks. So you could make a block of (1 long, 2 medium, 1 recovery), or (1 tempo, 2 medium, 1 recovery), (2 medium, 1 tempo, 1 long, 1-2 recovery), (3 medium, 1 tempo, 1 long, 2 recovery) … you get the picture. So depending how you are feeling for the last rides you kind of dream up the next training block on the basis of that.
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I would think that a good block for your training goals would go something like this ( 3 medium, 1 long, 1-2 recovery) alternating with( 2 medium, 1 tempo, 1 long, 1-2 recovery). But you should absolutely make your own, and change things up as you go a long. Nothing beats your own angle on your own body and your own training!
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About recovery. There is a very good idea to take easy weeks. The general rule is taking the forth week easy, or the third week, depending on what works best for you. But this is of course all about you and how your body works. So don’t be to preoccupied about what others do, but notice things that most every body do (then it might be worth while).
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Ps if we think of the distance in ratios of the LONG ride. Then for me medium might be 2/3 of Long and short about 1/3 – 1/2 of LONG.
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But in your case when long needs to be really LONG. ;) Your medium distance might be about 1/2 of your long ride. But the short ride would be proportionate to the ratio of my medium and short.
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These are of course very rough guidelines that you must tailor to your own needs and current form.
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PSS. Yes and another thing.
It can be very useful to think in terms of TIME instead of thinking in terms of distance. So you might measure your medium rides in terms of duration rather than distance. We both know that going over hilly roads in a head wind for say 100 km is totally different from going the same distance on level tarmac with a tail wind. ;)

I ridden in 3 double centuries. Just go out and have fun.