Since he was eating live before, just leaving a F/T mouse next to him probably won't get a feeding response from him. Wait a while - like 5 days - and then try feeding again. This time, feed in his enclosure (moving your BP from his home to a separate feeding container can be very stressful). Make sure that you heat up the mouse or rat to the proper temperature (rats are more nutritious, but it won't hurt to feed him a mouse). Then, using feeding tongs, dangle the mouse in front of your BP or you BP's hide. Don't hit your BP's nose with the mouse, btw. That can scare them into not eating. Make the mouse or rat do the "zombie dance" (just make it wiggle around and dance so it looks alive). If your snake doesn't immediately attack and you're worried about him eating it, you can leave the mouse right at the entrance to the hide. I find that any of my snakes who don't eat during the "zombie dance" will attack within a few minutes of the mouse sitting in front of their hide entrance.

Using these techniques, I've successfully switched all my snakes to F/T. And they've all made the switch to Rats instead of Mice. =] Just keep in mind that sometimes BPs don't necessarily want to eat - they can be finicky, picky, etc. As long as his weight is good, you have some time before you need to be really worried.