Member directory and user database

I realize Network+ is out of the WPMU Dev scope.
I am using it and I am making sub networks using sub domains and sub sites with sub directories. That is working fine.

My question is, how hard would it be to make the Members Directory plug in pull only the users that belong to a sub-directory instead of the whole database?
Currently it pulls from the whole database, so all sub networks have all user s listed.
I would like the sub networks and sub sites to have heir own group list of members.
Is there another plug in I should use?

Thanks for all.