I knew I forgot something. Yes, you can put unfiltered ACV (with mother of vinegar) in his water, 1-2 TBSP to a gallon of water, but dont put anything else in the water at the same time.
I'm sorry, I just now saw this. You should take away his pellets for a couple days and feed him plain active culture yogurt and scrambled eggs, soft things for example. Also, give him the oil soaked bread. Then let's see how he does. So far, sounds like you've done pretty well on your own.