Very simple.
If he is connecting from the owner's home we can safely assume it will either be from the same PC or a small set of known machines.
In that case, get the computer names.
Then change the logon script that runs for everyone in a TS (USRLOGON.CMD) and at the end add something like:
IF NOT %USERNAME% == "that_particular_username" Goto End
IF %CLIENTNAME% NEQ "Computer_Name" TSLOGOFF
:End
So resuming: check if the username matches the user you want to allow. If not, simply skip to the end (meaning do nothing). But if it matches it will go to the next line and check the %CLIENTNAME% (this passes the computer name the client is connecting from). If it does NOT match the one you want to allow, run a TSLOGOFF what will kick him out of the system.
Is this what you are looking for?
Cláudio Rodrigues
Citrix CTP