I’ve seen EJ do the hammer out of nowhere a few times, I don’t know if he does it every time though. The only example I can think of is at the 1990 Bottom Line NYC live show, during the song “Mountain Medely”. He plays a line in the 3rd position where he plays 2 notes on the B and G strings and then hammers on from nowhere for the 5th note in the sequence on the D string.
It is something he does a fair amount more with his “fuzzy” rhythm tone more than lead because it’s harder to head the difference between a picked and unpicked note.
The conclusion Troy came to was that he tried to use stringhopping to return to the start of the pattern but at faster speeds he would find himself making use of a “rest stroke”.
He would downpick the 5th note of the pattern and it would burry his pick in-between the strings but the advantage of this is that the higher string brought his pick to a stop. This means he didn’t need to use the energy stopping his pick and it allowed him to play faster.
He would just bury the pick and then try to hit the first note of the pattern and would (not consciously) slide his pick across the string in the middle to hit the first string of the pattern.
The episode of Cascade where he talks about this is free on YouTube if you want to google: The Skip Fives Lick (Cascade, Chapter 22)
This way of doing it is actually pretty intuitive to learn and only took me about 10 mins after I watched the cascade episode. It’s usually the way I do it simply because then I find I can synchronise my hands better and don’t lose timing at higher speeds.