That "tap on the snake" is a very common "trick" to make a snake turn & bite the prey you're trying to feed. BUT: don't over-use it- some snakes respond better than others- it's basically a defensive strike, & while some snakes will go ahead & eat what they bite, others will not. BPs are not always great with this technique, because they're usually shyer & mellower snakes, & more easily stressed.

I'm glad that has worked for you so far, but the need for extra stimulation likely means he's just not needing as much food as you've been feeding him. I'd suggest lengthening the time between meals, &/or feeding slightly smaller prey items for a better feed response. It does sound to me like you're overfeeding- -not to mention he's at that age when his growth is slowing down somewhat.

Overfeeding (esp. adult male BPs) once they become adults is a big reason they start fasting, which isn't fun at all. I'd much rather avoid causing a snake to fast, & even you seem to know these rats are a little too big.