This is a pretty amazing thread. The orignal question was whether a Panasonic TD system can handle an off-premise station, and the answer is YES.
The mechanics of doing it is a function of how and who is treating the pairs. Since the owner is installing 2 stations off his office system to a key system at his residence, you are looking at single line interfaces at the office FXO and station interfaces at his residence, FXS.
Call them OPX or OPS, it's just semantics. The function and mechanics are still the same. Back in the day, you ordered the facility from the telco, or ordered a dry pair and treated it yourself.
Today, with the Internet and VOIP, you can order your own FXO/FXS facilities for X amount of dollars and use broadband to extend your extension. An internet search of off premise extension will give you a whole set of links to the various manufacturers. One of my favorites (to read, I have not tried it yet) is
It's a pretty good site just to kick the tires and see what's available.
LkEErie