Training with ankle injury

[Eustace]

Starting approximately in June 2007, I noticed some pain in my left ankle, with reduced mobility the most noticeable problem. The pain would come and go, some days worse, others almost non-existent. In December I went to my primary doctor who ordered an X-ray, which found a problem, and the orthopedic surgeon I was referred to said that is was an osteochondral lesion of the talus. Currently I am on the waiting list for an allograft; I could have surgery in 2 weeks or 10 months.
My question is what should I do in terms of exercise, particularly weights? I've lost approximately 60 lbs, down to 250lb, and need to lose at least another 30-40. I've switched from walking to using the stationary bike and elliptical machine, with regular cardio and HIIT. I've continued upper body free weights, plus leg curls and single-leg presses with my right leg. What are the best options for exercising with this problem in terms of continued fat loss without exacerbating the injury?