Separate User management running on same Portal

Experts,

I was wondering if there is some way to have a separate user management running on the same portal.

We are running SAP Portal 7.3 today that is heavily used. Now we want to grant access for a limited set of users via a new url.

The tricky part is when accessing the Portal via that new url it should only see a limited set of roles.

So it is possible that a user has 10 roles using the standard URL and via the new URL only 2 of the 10.

Thanks,

Arnaud