Too bad I didn't see this post earlier. If your Zumo stores its map(s) in it's internal memory and takes an SD card, then you could've converted the gpx track into a transparent map onto the SD card. The map overlays any map you have on your zumo. Very inexpensive software to do this. http://www.gpx2img.com/
It works with Mapsource.
If you're familiar with loading maps to your gps via mapsource, then the converted gpx track can be loaded with other maps to internal memory of your gps. Remember to back up your original map first.
It is the gmapprom file in your unit, or gmapsupp on the sd card within a folder named "garmin". Also back up any gmapsupp.unl files and gmapprom.unl files you see. They are crucial to unlocking original maps. If you don't iknow what you're doing here, don't mess with it. Use the first option above.