I've found there are two very different ways of pick tapping. You can use the edge of the pick and just hammer it onto the string, if you release it quickly enough before the string looses energy it doesn't matter that there's no lateral movement to power the string in the manner of a real pull off. Alternatively you can use the tip of the plectrum itself and tremolo pick with the plectrum turned at right angles to the string so that the curve of the plectrum forces the string to fret with every up/down stroke. This sideways picking isn't so hard if you stary relaxed; it's a similar kind of grip to the one I use for pinch harmonics actually, but with a slightly greater angle between the pick and the string. This method creates a shorter duration higher note than the traditional way but is freakily fast.