I figured out how to do this using ArcGIS relatively painlessly, but it would be a lot easier if Garmin would allow for this functionality
I don't use the camera for action shots like it's marketed for but rather for documenting while simultaneously collecting the 'where' information (geographic file). Here is a link to a video where I use an aerial imagery file (not Google imagery) as a background for the track gauge. I also change the location of the gauge in the frame at 23:00.
I´ve seen videos, where somebody just took a Google Maps Screenshot and overlaied the map in Edit.
You have to play around with the Zoomfactor and rotation until it fits, but it also should work.