Make a Dwarven Frenzy freak and give him heavy armor. When the badguys are dead, everyone runs away and uses their faster movement to avoid friendly frenzy fire.
Or monks giving out a lot of subdual damage to "calm down" the frenzied berserker...
This is Standard operational Procedure to subdue possessed or mentally controlled friends. Monks and Rogues with Saps are the best to take down out of control colleagues...
Berserker in town shopping session: "Hey guys...what are all these saps and sleeping poison you are buying ?"