Interesting conversation.
Here's the problem with that, however.
Page 304, under Spirit of Man Optional Powers.
Fear, Innate Spell (any one spell known by
the summoner; Force is limited to spirit’s
Magic),
This seems pretty clear that the spirit of man (in this example, at least) can only choose from the spell list of the summoner. I just dont see a different way of reading it. Did I miss something?
Plus, A4BG's idea of having a spirit maintain a spell is for all points, spirit slavery. It wont take long before you start earning negative 'relationship' (for lack of a better word) with that spirit type. Sure, it will work on a mission, but the longer you force a spirit to do that, and the more frequent you use it ... you're going to be pissing off lots of entities.