I thought I tried a compressed timeframe...........Are you applying for class of 2014 for entry in fall of 2010? If so, thereis certainly no problem with waiting a month or two to take the MCAT.
I tried a similar strategy (took physics I and II over a summer) and tried to take MCAT without OChem II and without any BIO (I know....). I am embarassed to say (but I will so hopefully it will help someone else) that I got an 18..........Needless to say, I did not get in with those scores.
I retook the MCAT after having some Bio and OChem and it worked out fine.
Even if you do get the classes, you will need time to review everything AND take several practice old MCAT exams to prepare, IMHO. I would take your classes, spend a month reviewing and traking practice exams, then register for another (I think you have to wait 30 days). This will give you all the experience and also set you up to retake in Sept if necessary, which you can always cancel if you do not need.
Whatever you decide, do not discount the actual circumstances for the test. Although nothing can stimulate that feeling, taking practice tests under simulated testing conditions will be as close as you can get........................unless of course you are my nephew that comes home from a month abroad, takes MCAT without any prep and greases a 38 (wtf??)
Good luck.