Bob's definitely done some specific magic tricks, though they all are one the less tangible Spirit side of things, by and large, like controlling host bodies (animate or inanimate) or shielding people from spiritual attacks. Though he apparently can access the spells laid into magic objects and control/enhance them to some degree, and Evil-bob was able to cast a necromantic attack once, as well manipulate the NN enough to set up defenses to a particular location. All this to say that there is, I think, a dividing line between what he can do and what is available to a full spellcaster, but Im not sure where that line would fall, and it could likely be different for another spirit like him.
My bigger question with Sponsored Magic would be to wonder what the Sponsor would be getting out of it from a Spirit like that, can such a creature develop the sort of debt that would interest the sponsor, and how would they have to go about repaying it. It would be complicated for bob, but maybe not as much for a spirit that is not Bound to the skull and the will of it's owner the way bob is.
