Easiest way to go is to rub a crawler rat in mouse pee, and offer it up that way--they often start to eat it before they realize there's a difference, and frequently take the next one unscented, since it's now more familiar.

I've also had luck with offering a rat the size of an adult mouse immediately after feeding an adult mouse--this works on snakes used to eating multiple mice. They eat it before they realize it's not a mouse, lol.