Promotions based on reputation, how to reserve (demote)?
 

I've created an additional usergroup with privileges to access one specific forum. I created a promotion that says when a users' reputation points total are greater than or equal to the specified total, add the additional usergroup to their privileges. Simple, right? Yup. And it works fine.

Questions is, how can I reverse it such that if a user falls below the specified reputation points total their additional usergroup privileges are automatically removed?