Role based group administration?

I have a large site using OG which is 95% complete, but I have just discovered that I cannot moderate the groups in a way that seems logical to me.

Currently, the only users that can moderate group membership are the person that created the group, and admins (user 1 and any users in the role created by admin_role module). Obviously, I don't want people to have the admin role.

However, I need for the group memberships etc to be managed by any/all users of two roles - I would have expected that the "administer organic groups" permission would allow this, but it does not!

So I'm stuck at the moment with no mechanism whereby this "group admin" role can be assigned permission to moderate any group membership. I really need this. It strikes me that I could potentially do something with Rules, but it would be very ugly indeed.

Is there some way I can hook into OG and generate this permission or override something? I'm pretty screwed if I can't do this, and obviously I don't want to start hacking away at core OG code...