Is it possible you put way too much motion into wiggling the prey when trying to feed with tongs? Because that will scare many snakes (especially one that had bad experiences with live prey, maybe even before you got him?) if you don't do it just right. I find it hard to believe he's actually afraid of the tongs- snakes don't tend to notice such things at all. BPs rely on their heat sensing pits, so it's more likely he's afraid of your nearby hand (or specifically the heat signature) that's holding the tongs.
Also (when using tongs) never approach the snake with the prey. Instead make it appear to cluelessly pass by, just out of reach wherever the snake is hiding, & keep the motions very slight & subtle. In the wild, no rodent is going to approach a snake & volunteer to be eaten.Such bold activity does scare some snakes, especially shy BPs.