Although a standard 12V socket would work fine, I've done this a lot in the past and found it can work loose on long trips (Powerlet seems to hold much better if you want a socket of some sort).
I just soldered on an SAE plug (that 2-pronged plug you see on trailer wiring - available at any auto parts store) to the end of the bare wires that come with the Zumo connector. Since I already have a battery tender wired to the battery (which has an SAE plug on the end), I just plug my zumo into the SAE plug for that. I also have a small air compressor that came with an SAE plug, so I can plug that on instead if needed. My battery tender plug runs from the battery to underneath the seat (with an extension piece) and the zumo easily reaches from the handlebars to the seat. I lift the seat and connect up things as needed (battery tender/GPS/compressor - you'll never need all of these things at once!).
BE CAREFUL if you do this though. Make sure you wire it so the red wire from the Zumo ultimately leads to the + on the battery. Makes sense, but I've seen this done backwards before.