I agree 100% with Deborah. If they don't eat, they don't poop. Yes, they'll use their body fat, but it doesn't end up as poop. Poop is undigested food (or rather food that is undigestible). Body fat was digested the first time around. The one thing I would add is that you should try an even smaller meal until you get him going again, then you can bump him up to a small. I would try a weanling rat. If that doesn't work try mice. When they don't eat for an extended time, their beneficial flora that aids in digestion dies off. A much smaller meal will be easier to digest, and get the flora going again. It sometimes seems that the snakes "know" this and seek out smaller prey items.

I have a male that has been on a fast since last september. A few weeks ago, I finally assist fed several mouse pinkies, yes, pinkies. The snake isn't going to get much out of those, except to rebuild the flora. He took a weanling rat last night. That was the first voluntary food since september!

Oh, couple other thoughts. Are you feeding late in the day? Balls are nocturnal, so sometimes feeding at night will help. Finally, weather can sometimes play a role. It was storming last night when my fasting snake finally ate.

Good luck!
Steve