Well, totems can just be treated as focus items, for most intents and purposes, I think. A character aspect, if the shaman in question is bound to any particular totem animal would also be appropriate. You could borrow the "echoes of the beast" power, to represent a totem animal even further, giving the shaman some skills of the animal in question.
You could take any of the powers in the book and treat them as highly specialized spells. Beast change and such have already been mentioned, of course. Gaseous form, for example, could be the shaman's way of a spirit journey, and he is so good at it, that he merely needs an effort of will to leave his body.
Depending on how much in line with history you want to stay, you might only have thaumaturgy available for your spellcasting tribesmen. On the other hand, that frees up tons of refresh for refinement to really make those rituals count. You could also come up with a couple of stunts for cooperative rituals, where 2 or more people cast a spell.
Another idea would be to combine spellcasters and true believers, since shamans are kind of both. that means you can adjust the true believer powers for your purposes. Even if it is not the white god that is helping them, animal spirits or manitu or whatever should work just as well, as long as they believe in it.
Sponsored magic might also be something to look into, especially in conjunction with true believer and totem animal. The magic is already colored by the sponsor, which would be the totem animal/animal spirit in this case, and the rest only furthers this connection.
Granted, this is all from Native American tropes, I don't know much about them outside of that. I would recommend you search the internet or browse your local library, if you are concerned about more accurate details about them. Once you have those details, you might find it easier to flesh them out mechanically. If you still have problems after that, you know where to find us