Here's another option.
Buy half a metre of 7-wire trailer cable and a flat socket to suit. Peel the covering back on the cable that runs to the NATO socket, work out which 7 wires you need and use joiners/solder and heatshrink and tap into them. If you insulate it well you shouldn't get shorts or corrosion of the wires and you can mount it somewhere in the open or tuck it up underneath if you want it to be inconspicuous.
Whole job would take and hour and around $20. Also, if you ever need to tow something with a NATO plug, you still have the original connected.
Greg.