Haven't taught this either, but my thought is that I'd stack mats a little higher than the level of the vault table/any sort of mat setup they could "vault" onto, and see how well they can do the half on/half off there to their stomach. They are going to need to twist from around this position. For a half/full I don't think intense twisting initiation is necessary for sure, but I have known very few people who competed handspring on, double twist, and they seemed to wrap (with little instruction since this vault generally isn't intensively taught at the higher levels) the way a diver would, which I find interesting.