Allison -
How big is he???

In addition to what Becky said, you may want to give him some Bene-Bac for Birds and Reptiles after the flagyl and before the mouse. This will boost the beneficial bacteria in his digestive tract, which is most likely very low after regurge and not eating for a long time. Oh, if you don't find Bene-bac in the reptile section, check the bird section. I have gotten it from Petco in the past. It comes on a little hang card with 3 little tubes on the card. The Flagyl and the Bene-bac could possibly boost his appetite to get him going. If not, you may want to assist feed SMALLER than appropriate sized mouse until he does get going. Offer it to him live first, and if he doesn't take it, kill it and assist feed. You'll want to get him putting on some weight, so feed every 3 or 4 days until he picks up on his own. Once he puts on some weight, and gets a little stronger, he will most likely become more confident and surprise you by eating on his own.

I've had very good luck doing this with several problem feeders, two of which I'm sure would not have survived otherwise.

Good luck!
Steve