Congrats! And lucky! I'm still trying to get mine off his fast. As to how often to feed him it depends. If he needs to gain some weight, I'd stick to how you were regularly feeding him before, then maybe after a couple or so times, or more in the summer time feed once a week, maybe with a little bit smaller sized rats though. Not sure though, I haven't successfully managed to get my BP off his fast yet and this is the first fast I've experienced so.
Although, I have rescued some BPs(as you can tell in my signature) and if they're underweight, depending on how weak/neglected they were and what size they are I try to feed once a week.