How big is he again? If he's an adult you can do like Diamondill said and kill one and give it to him fresh. He might just not want to eat a live one because he's been bitten before or because it's frightening. I've had babies that were stubborn eaters and they were terrified of live pinks.. so I ended up just trying different methods. Have you tried partially skinning a frozen/thawed or fresh killed mouse? It's the same concept as slitting, just less messy since there is no blood when skinning.
My female that I got last week that has never eaten f/t in her life took a f/t adult mouse today, I just had to heat it up hot and blow dry it, then zombie dance it gently.