Restrict to initial NAS used to logon

Hi, Looking to restrict a user to only be able to log in and re-log in to the initial NAS they first ever logged onto. (Hotspot) Looking at the radacct file where it looks like the check-items normally go against, I'm not seeing anything I can use as an identifier. The nasipaddress is always 0.0.0.0. Maybe calledstationid, except if we swap equipment out during the lifetime of a users id it won't match. Is anyone doing anything like this already? Thanks, Tuc