I think melee with some limited casting, but to give them their own little "I am special thing" give them an ability that makes their next spell aoe, and one that makes their next ability(not weaponskill) aoe. So they could do things like cross class invigorate, and make it be aoe, or they could aoe Second wind, internal release, or whatever depending on the classes they can pull abilities from, or one of their own abilities. Keep a decent cooldown on it so it's balanced, and they would need to decide which abilities would be best to aoe and when. For spells you could give them some simple debuffs, paralyze and what not, and the aoe spell ability could make it useful for groups.