I was doing bodybuilding before I went for LL too.
If you're talking about maintaining your upper body muscle mass, I'd say it's possible. But it is a very difficult task. Unless you have lots of motivation and a desire to really maintain your muscle, you're probably gonna lose most of it.
I didn't touch any weights for the first month I returned home from LL. (post-op) and that alone had caused me to lose quite a lot of strength/muscle.
But the good thing is that I have a gym set at home (free weights, barbell, power cage etc). After one month I found some determination to at least work out whatever I can. trust me, when you are not fully weight bearing, the number of bodybuilding exercises you can do is so limited. I stuck to bench press, shoulder press, lat pull downs, and simple arm exercises. It's pretty obvious and easy to figure out what you CAN do and what you CANNOT do given the limited weight bearing. And even if you're on a 'weight bearing' method, you surely won't want to be standing up with those weights anyway. I stuck to a 2-3 day split to workout whatever muscle groups i can, obviously no leg exercises. I managed to keep going for a couple of weeks.
It takes tremendous discipline and effort to stick to a gym routine while doing LL. Don't forget you're probably be on a daily stretching and therapy routine for your legs too. That will take time and energy too. While for most LL-ers time is probably not a constraint but you have to factor in mental strength, discipline and willpower. After forcing myself to work out for about several works, I finally decided that it was not worth the time and mental strength to be struggling with muscle mass or body aesthetics. It was also very inconvenient to even get onto the bench and have SOMEONE else load the weight plates for me. (Yeah, if you're doing bench presses you're probably not able to load the plates yourself.) It was a great hassle and don't forget I had my gym equipment like several metres away from my bed.
Of course, it can be done. After all I stuck to it for a couple of weeks. Worked out 3 times a week. But if you still care about your upper body muscle and what not you're going to have a hard time. LL is already tough mentally and the last thing you want is a concern or being depressed over losing your muscle mass. My advice? Unless you have unlimited energy and will power, go ahead. Else, let it go.
In summary, LL is not going to explicitly stop you from doing bodybuilding (I'm talking about upper body here) but every small thing will suddenly become inconvenient. And don't underestimate this. Also, having sore chests/arms and having to use your arms for loading/transfers/crutches is also not a good feeling. If you do LL, just focus on recovering first and then think about the muscle later. You probably won't be having much of a social life during LL anyway, so who cares if you lose all that muscle. If you already got the muscle, it shouldn't be that hard to really regain them when the time comes right?
That having said, I'm just a guy consolidating. Have given up on lifting weights for now and focusing on my LL. Will probably only resume a routine / diet once I get full weight bearing status. Just my 2 cents.