I don't know how helpful any of this is for your situation, but here's some info from Susanne on remedies/supplements that can help with digestive problems and ordinary yeast in babies. Some of the items are unusual but there are others that you might have in the house, like lemon juice or chili powder:
http://tinypic.com/useralbum.php?ua=MNW ... F7fw%3D%3Dhttp://tinypic.com/useralbum.php?ua=9f% ... G0bA%3D%3DSusanne doesn't like vinegar, but I suspect it would have pretty much the same effect as lemon juice. I tried to ask her about using these things with your birds, but it looks like she has already gone to bed. If these were my birds, I would give them a small dose of anything she recommends that I had on hand. I don't think it will harm the birds and it might help counteract the yeast a little bit (if that's the actual problem here; it would help fight bacteria too if that's the problem).
If his energy level picks up noticeably you can stop giving the electrolyte formula - it wouldn't be good to overdose on salt. But you can keep giving him sugar water if he'll take it, or honey or Karo syrup. The best-case scenario would be if he started eating some solid food, but if he doesn't then the sugar will provide some calories and energy.
I have to go to bed myself now. Tell those bad boys my whole flock is sending positive thoughts their way, and they need to get well fast!