Little update on this picky guy. I think I've only had success once feeding him a rat without first scenting his cage with gerbil (and hamster once). He completely ignores mice surprisingly, and is eating another small live rat right now. I bought a gerbil to feed him a couple weeks ago, but tried giving him a rat first. He ate the rat, so I decided to just keep the gerbil as a pet and use its dirty bedding to scent rats for him for the future. If he absolutely refuses a rat even when scenting, I put him and the rat in the gerbils cage (I remove the gerbil first) and that seems to get him to eat it.

Hopefully I can get him eating rats without scenting and without having to move him.

He's a year old and has gone from 250g to 400g now. He will only eat for me about once every 12 days.