Allies and sustaining foci, Inhabiting, manifesting, bonding Options

[Talia Invierno]

Allies automatically have Sorcery and at least one spell they can cast. There is nothing in canon to suggest that an ally doesn't have the same TN penalty for sustaining a spell as any other spellcaster, although there might be a suggestion that the ally can sustain a spell for the caster at the same time as doing its own thing.

Can an ally bond a sustaining focus? More drastically, can an ally be conceived to inhabit a sustaining focus, and be able to take full advantage of it? Heck, can one of the forms of an ally be linked directly to a sustaining focus, with the intent that the ally should be able to use it? (I draw the line at it being that focus, since in a way it already is. I'm talking about linking an already existing focus in with the ally's formula.)

Would there be any limit on the rating of such a focus, while still being fully usable by the ally? Could an ally become subject to focus addiction?