if he's being picky then now isn't the time to do the switch. i say get him to feed a few times consistently before trying to switch. also, some snakes are shy eaters, offer them a hide in their feeding enclosure so they don't feel "exposed" and offer the food in front of the hide. i offer live fuzzies in a small brown paper bag, laid on its side. this allows the snake to go into the bag to feed and it's a smaller area so less exposure stress.

why are you wanting to switch to f/t anyways? of the 4 people i know who own BP's (including myself now, making 5 total) we've all experienced BPs being picky, especially when it comes to trying f/t. my baby wouldn't feed on f/t, tried live, wouldn't feed, tried the brown bag trick, works every time. she's almost conditioned to know that food is in the bag now, if i put an empty bag in her feeding tub she goes right into it.