Weight loss exercise without using legs?

[Cylenia]

I have really been trying to lose weight. I started the "Jenny Craig" program to modify my diet, cut out sodas and alcohol, increased water intake, even stopped the coffee, and tried to start an exercise program. The problem is that all the exercise programs I have found for burning fat require lunges, squats, skipping, jumping, etc. that really stress the knees. My knees are in very bad condition. Even walking over distance causes swelling and pain. Doc wants to do TKR on both legs but I am trying to put it off. What fat-burning exercises are there that do not require weight bearing exercises with the legs?