Category-Specific Roles?

I'm managing a server for a dnd club with multiple campaigns/player groups each with their own categories, and it's recently come up that someone who's a player in one group wants to dm for another group. I have both the player and dm roles set up already, but although I trust the person, I don't want to give them dm-level permissions in the category they're a player in, for I think obvious reasons. Is there a way to give this person the player role in one category and the dm role in the other category, or will I have to artificially set it up somehow?