Basically i bury the PB,s in s/h the same as with bark.I have done this with numerous plants/species without problems.Phragenstein had it,s first growth buried quite deep but a new growth still has managed to come from it.
I have a Onc Aloha Iwanaga "Dogshima" that has PB,s about 4" in the air , all i do is guide the aerial roots to the medium.Same for Onc flexuosum.
They are both growing new PB,s so they don,t seem to mind !