Since you can't change your schedule, I'd try something like a calming tea or other drink, or some relaxation exercises. I have a 20-30 minute PM Yoga on a DVD that's all about winding down the day, something like that might work (or you could use the AM Yoga to start your next day when you're still yawning -- arguably cheaper/better than coffee ).

If you are eating or drinking during/after exercise, that could be a part of it, too. I've found if I eat sugar or drink caffeine too late, I can't sleep and when I finally do, I sleep poorly, even if I exercise or go for a walk to burn the energy off.

And, if none of that works, lots of pre-race-day jitters guides seem to recommend sex (and, I presume, related activities) as a good relaxation technique...