To expand a bit on Boiler's reply, Leviton makes a single address transmitter that looks exactly like a standard Decora switch (HCC10-1TW). It does not switch the load itself, but just needs access to power. It transmits a signal to another another X10 compatible switch that actually switches the load. You can get one for $35 plus shipping on eBay.
Sorry to take this thread onto a tangent, but Wow, thanks! I had ever heard of these before.
While not possibly a solution for the OP, this is certainly a solution to a problem I have had for years. In my bedrooms, the wall switch by the doors controls the outlet which is also just by the door. That is of little help since that means any lamp plugged into that outset would be by the door too. I could just as easily switch the lamp on/off by its own switch.
What I really want, is to be able to turn a lamp that is elsewhere in the room, on and off.
The wall switches have only two wires running to them; hot and hot return. However, it would be a trivial re-wire to change that to hot and neutral; just what these Leviton single unit controllers require.
With these Leviton controllers installed, I can use them to control any X10 module anywhere in the room. Plus, since they look like familiar Decora style switches, others (visitors, guests, etc) would not have a problem using them.
Again, sorry for the tangent, and thanks for the info!
We now return you to your regularly scheduled thread.