How to add 'sub-admin' to custom user groups?

[headkit]

Hi!
Great package, thanx for sharing!

I want to add a 'subadmin' to administrate their subset of users collected inside a specific ROLES group. So I made my first user a 'superadmin' in Roles.GLOBAL_GROUP to make it administrate them all.

superadmin (also admin in Roles.GLOBAL_GROUP)
    admin A (in Roles.GLOBAL_GROUP and in a custom group)
        user 3 (some role in a custom group)
        user 4 (some role in a custom group)
     admin B (in Roles.GLOBAL_GROUP and in a custom group)
        user 6 (some role in a custom group)
        user 7 (some role in a custom group)

how is the best way to make the 'admin' role only get access to users of their own ROLES group? and how could we restrict acces to specific collections in the left navigation bar of the admin panel?

thnx!!!