hi
i think you are pointing here about framing the ips or routes to a particular user id or profile.
we do this normally with the ISDN connectivity over here where we mention which block belongs to that particular user id and which static ips he can use up for his internal servers like citrix or mail though his wan ip being assigned from the SP pool and it may vary time to time.
So the binding is done with the user profile based on the user id stating that the static ips belongs to that particular user profile which makes convenient for the user to use the static ips in their local lan.
regds