Hey.
I've been doing pull-ups everyday since week 3 of lengthening (I'm in week 6 now). I couldn't do it before because I lacked the mobility and the drive to do so.
The key is when you lift off and when you finish - make sure you're very very slow putting your legs back on the ground. You don't wanna put too much weight on your legs too hastily, or risk falling. I do about 15-20 pull ups a day and considering I've lost so much weight since the surgery (about 17 lbs) I do see some definition preserved in my arms.
Believe me, I miss lifting too but that's the price you pay. Don't go too hard and give yourself at least 2 weeks of rest after the surgery...you don't wanna strain your body during that period, it's using every bit of energy to fix your legs. You'll be back in the gym soon enough - just taller
Cheers.