The Speed Pulse Generator worked perfectly. I included a bypass switch so that I can disable it just in case. At this point the device makes the NAV think it's on a ferry. It acknowledges movement, but only short 1km/m movements. Enough to keep it unlocked, and allow the NAV too keep updating the map.

The down side is you have to bypass it to watch a movie. Each pulse makes the screen flash black when in DVD mode.