Dont know if this has been posted, but since he is WC, try gerbils...they dont eat mice in the wild, and very rarely do you NOT have a problem switching prey items on even CB balls.

You said you tried hamsters, wrong route...try gerbils.


***Edit*** Anybody can correct me if im wrong, but as far as i know, gerbils are their natural diet when they are wild.


Hope that helps!