what do you do? there's no possible way I can eat the 4000 calories recommended in bodybuilding magazines. how do you do it?

You don't. Try and eat as much as you can though. One way to do this is a few ounces of protein centric food every 2-3 hours (once you are far enough out, like 6-7 months). Even then, you will only hit around 2000-2400 a day which is just enough to build some decent muscle, but nothing on the scale of a pumped up body builder (I think). If you do end up eating a lot of calories for a WLS person, make sure you have enough activity to balance out those calories. It would be very easy to gain weight (not muscle) if not careful about balance and quality of food. My two cents.