Hmm.. I wish I could be of more help, but I am unsure if my advice would be good or not.
I know when I had surgery on my lower abdominal area, I couldn't move very well and had to stay kind of hunkered down when I walked or moved for days and at the time I was taking care of my sisters kids full time and I hurt my back. Every time I moved it hurt and I'd groan.
I think "doggy-style" worked best because I could control how my back moved a little and there was no pressure on it as long as I didn't arch my back.
But if the male has a hurt back, I'd say doggy style could be a less painful way to go as well. Maybe stand straight up behind her/him and let him/her be on all fours on a bed or something that will make it to where you don't have to bend your back too much. Then, you can just use your hands to do the guiding instead of using your full body to thrust.
You may have to take it easy and slow until it gets better, but that might help. I hope so anyway
Hope it's better soon!