After seeing my precious baby normal (well...she's 400g) get a few scales shaved off by a rat (because I wasn't quick enough with the tongs) yesterday, I'm considering feeding pre-killed. When I get a place of my own, I'm going to breed my own food and use a gas chamber to kill them first.
If he's eating rats and taking fresh killed, I'd feed him that. You can also try to feed him a F/T rat.