Yup, my vet looked in her "exotic animal medicine" book and it listed dosages for Flagyl and mentioned that it often acts as an appetite stimulant. She gave my snake 1cc (100mg) by mouth via a syringe with a small feeding tube attached. The snake didn't really care for the procedure but he held it down.
Now I figure I'll wait till this weekend and offer him an ASF again. The vet and I decided that if that didn't work we would try another dose next week.