I have an 8 year old jungle carpet python that refuses to eat anything but mice. I've tricked him twice into eating a rat. The first time I believe it was mostly just dumb luck and a hungry snake. The second time was when I was finishing up feeding the rest of my snakes. I buy live and kill them prior to offering them to the snakes and had just emptied a small tub of mice. I put a small rat in that tub for about 15 minutes or so while I was finishing up with some other snakes. When I retrieved the rat I noticed it smelled very much like mouse urine so I offered it to my reluctant snake and he struck and coiled it instantly. Unfortunately, I haven't been able to replicate that scenario since and have to feed him half a dozen mice at a sitting.

I know how aggravating it can be to have a mouser on your hands. Hopefully you'll get him switched over. I'm crossing my fingers for you!