There may be an earlier origin of Hocus Pocus than your conjurer. I remember reading (I thought it was in one of your books, but obviously not) that “Hocus Pocus” was used by an early Protestant theologian to belittle the Roman Catholic doctrine of Transubstantiation, that the eucharistic host (the wine and bread) actually become in fact the body and blood of Christ. He was saying, in effect, that Transubstantiation is so much “Hoc es” Pocus.
I am by no means a scholar or acedemic, so I can’t offer any citation, just my memory.
Daniel R. Harwick