Re:broken ankle question
I read somewhere, a long time ago, that if you do strength training on one limb, the limb that is not being actively trained will maintain muscle strength longer...and maybe even gain a little strength as well. Haven't seen anything recently so I don't know how accurate that is. Even so, I think I would still be bothered by the feeling that I'd be lopsided. Can you do isometrics for the casted leg?
Perhaps a physical therapist (esp one who works in associate with an inpatient hospital rehabilitation program) would know of specific exercises.