I'm uncertain if brown snakes are any different, but the neonate garter's I've fed in the past all did really well on worm peices and guppies. Just watch for accidental cannabilism. They can get a little crazy when there is the scent of food in the air.
The disease reason for the laws are quite a valid reason IMO and is based on the common mix of people keeping many snakes from a diverse geoscope and not having the know-how or facilities for quarantine. Any snakes that are to be release into the wild (or parents thereof) need to be kept in strict quarantine for the aforementioned reason. This can be as simple when there are no other herpetiles in the household. Many pathogens do not necessarily always present as disease, therefore even with a veterinary exam you very well could be sending an ecological timebomb out the door.
Now that I've shared my vantage point, if done responsibly, your idea is a very good one at that
Ian