Get the largest live fuzzy you can find. Fortunately a fuzzy is too small to hurt a snake so you can leave it in the tub with the snake for a while.
Offer the feeder just after sunset, this is when BP's normally become active as they're nocturnal hunters.
Also this breeder didn't do you or the snake any favors, a hatchling that has never taken a meal should not be sold, especially to someone who is inexperienced with starting a baby.