The way I did it was to make multi site users hot desk extensions. Make the teleworker set CESID their home DID so it reports that address. Make COR for the teleworker not allowed to dial anything but 911. This will force the user to login as their hot desk extension, but 911 calls get the CESID from the base extension NOT the hot desk. Then when in the office you make that phone a different base extension with same COR that only allows 911, but the CESID of the office.