Depends on the snake. Some will take food no problem and some won't show any interest at all. You can try to offer him food and see what he does. If he refuses, don't waste your time next time around.
Yeah, just offer the rat/mouse. If he strikes he'll eat, if not he won't. I've fed my snakes in blue before just to wake up the following morning to a fresh shed and a massive turd... Guess it helps speed the process for some hahah.