I don't know if this will help but I've had to nurse a few chucks back to health....
Its been a couple of years but I cut the end off of a 1cc syringe...so it was a hollow tube with a plunger.... I mixed up some canned dogfood (yes I know bad...I probably should have used baby food, but I wanted to get protien in 'em to fatten them up) with origional peadilite (baby isle)....I like peadilite better than gatoraide because it is designed to re hydrate babies that have have diarreha..... plus it doesn't have any "flavor" added if you buy the clear/origional formula (it does expire really qwuick once opened).... I also mixed in some vitamins....
Sometimes you can rub the bottom of their jaw to get them pissed(ie OPENING THEIR mouth)...then you can put the syringe into their mouth...they'll usually bite down on it.
If not, you can try prying their mouth open with a credit card/drivers license.... be careful not to cut up their mouth doing this... a skinny chuck with moutth rot is even worse!
The beneficial bacteria they are talking about is availiable at most pet stores...its called "Beneabac" or something like that... People use it with small animals, birds, and herps!
Its alot of work, but stick to it...theres nothing else you can do.....
PLUS your on a good fourm with lots of experienced chuck keepers!
Graham