Well one thing I was thinking was that it could be player choice. Hell, some people actually want to use an evoker o-o
As long as it's something that actually gets the point across well and isn't totally random, then it shouldn't be too hard to come up with something. Hell, injecting yourself with adrenaline would give the same effect as an evoker.
The real problem is people picking personas, though that could be a first come first serve thing. I'd personally ban god tiers like Mara or Alice or w/e
Baa baa black sheep have you any booze? No sir, no sir, I'm a....sheep~