VC needs a "Role" object, you would assign permissions to roles instead of users. Then, instead of creating users, would would select AD Groups/Users that can access VC, and assign one or more Roles to that "User".
One way to implement in UI would be to convert the VC "User" object to a "Role" object and add a "Members" collection which would be the AD Groups/Users. Would need a special fixed Admin role with all permissions (cannot change permissions on Admin role).