Yeah, good idea to leave it in the tank for a bit. Maybe he needs more time to try. Our BP eats F/T happily, but we notice an occasional pickiness if it cools down too much - if the warmth it gained dissipates too much. So we take it out again and hold the mouse head-up toward the CHE - this allows the entire body to warm up more, but especially the head, as Derek said. Mammals heads are the warmest part of the their bodies, and snakes know that. It also helps them find the head easier and swallow faster, instead of having to move their mouth slowly along the body and up to the head.

How were you feeding live? Can you try to make the F/T process similar in more ways - like how long you leave it in?