I have a site with a few security roles. I'd like some users to be able to subscribe to a security role, but not others.

For example, we have Teacher and Student security roles.

I want to have a Teacher directory, but with only with an Opt-In option.  The module I am using allows for displaying members by security role.

So, I would like Teacher accounts to be able to subscribe to the security role: "List Me In Public Directory"

However, I don't want students to be able to subscribe to that role.  

In other words, only allow certain security roles to subscribe to other security roles.   I guess one way of doing it would be to put an RSVP code that only teachers could see... but that just creates confusion for them, I think.

Hope that makes sense.  Any help or thoughts would be appreciated.