Make do with what you have. If your lower body is shot, work on your upper body. Sure cyclists don't need a lot of mass there, but it still doesn't hurt to build a few lean muscles up there. It'll also keep your metabolism high when you work out, so you don't get fat while you're off the saddle. So just go to the gym, do a few bench press with very low weights but with very high reps (this will get your heart pumping). Go do some serious core (abs) workouts, all cyclists need a strong core, it is your 'core' after all. Work on your flexibility as well, so you can stay in a more aerodynamic position for a longer time without getting back pain. And if you still have time, pick up a book and learn some proper cycling techniques.

See, look at how many other things you can do in the meanwhile. There's really no point in sitting around and moping, so get to it!