Torn Ligament in Thumb, Training Suggestions

I’ve been diagnosed with a torn radial collateral ligament in my left thumb and am planning surgery in the next few weeks. MD and PT tell me about 12 weeks for 100% recovery, but I’m hopeful that I’ll be able to do at least some lifting and conditioning work during that time.

Does anyone have suggestions about exercises or routines I could do while by hand is in a cast? Any supplements I should consider taking to assist with recovery and/or minimize muscle loss during the layoff?