wholesale issue

[Ashraf Al-Basti]

Dear All,
i want to setup a freeradius as a proxy radius for a wholesale, and want 
to limit the access by using the calling-station-id; so user1 at isp1 can 
connect only from any calling-station-id that belong to isp1, (ex, 
555111, 333222) and user2 at isp2 can connect only from any 
calling-station-id that belong to isp2....
i have all the calling station id which belong to the ISPs, but i didnt 
have the username for every ISP, and want to  use the realm instead of 
the username to do that.
can i use the checkval to check for the calling-station-id and realm, or 
is there anyway to do that?