Can we limit users the ability to create groups?

We are encounting a dilemna where we have users that need to be able to supervise their own groups, but because they have the Group Supervisor role, they can also create groups. We want to limit their ability to create new groups.

So how can we allow users to manage their own group, but not be given the permissions to create a brand new group (and delete a group as well)? We really want to give users the ability to just manage a group that they are a member of. That is all.

Thanks!!!

-Kevin