If possible have all voice actors run a set of predetermined "spell chants" as the verbal components for spells (every spell an unique one).
I seem to recall that casting spells in BG1 and BG2 had nice verbal components and its this that I am missing in BG3
This is in game already. Have you not cast any spells or witnessed any being cast? I think it's not every time due to reducing spam. I've bene impressed thus far with the various spell incantations.