I would agree with most of this, except the part about leaving live in overnight. I just don't know about that...I have a hard time leaving the room when there's a live prey item in my snakes' tub (although I'm feeing items a bit bigger than pups...), and I'm a bit over protective like that.
I would say maybe dim the lights (so you can still sort've see the rat) and sit very still within eyesight of the tank. If he doesn't take it within an hour or so, I'd consider it a no-go and pull the rat. Unfortunately at that point you either have to (humanely) euthanize the rat and freeze it or feed it to someone else.
Good luck!! Hopefully he takes it!