If there isn't one already, or maybe I am just overlooking something, is there a plugin that would allow users to have two ranks under their name. Say like a Moderator rank and also a Donator Rank?
Mybbcentral has a plugin which displays additional user groups on member profiles.
Mybb.com has a plugin which displays additional user groups on postbit. - http://mods.mybb.com/view/show-additional-group-images
Take your pick.