>>Well, could I feed it anything such as veggies or other foodstuffs for it? There is no real "local" pond here, so if I let it out it would probably be my backyard (I've found a few frogs hopping around there too).
Bullfrogs are insectivores (crickets, worms, etc.) so it would need them in some form, either live, dried, something. They prefer their food moving when that's what they're used to so it could be a task getting them to eat anything else. There are places on-line where you can buy 1000 crickets for less than $20.00 (like wormman's) to save money. If you do you'll need a 20 gallon tank and egg cartons to house them.
As for letting it go in your yard since it's been captive it may starve while trying to figure out where to get it's food. A local stream might work as long as it has some deep places in it. Or you could see if a local pet store would take it, or put an ad in the paper. Remember it's counting on you to take care of it now.