Quote Originally Posted by Sausage
This is going to sound terrible, but you can slam them on something, which should kill them instantly. To stun and not kill, maybe putting the rat in a dark bag and shaking him a little or something might help. That way, I think, it should be disoriented enough for the snake to get him without any trouble. I just thought of that randomly... don't take my word for it.
Neither humane nor particularly well thought out. Lets remember these are living creatures too. The answer is, feed nothing bigger than a small rat.