There is a workaround that works for all types of gps.
Once learned it is quite easy to do.
The method is to produce a "trackmap" that has a transparent background and thus will be seen over the original map.
Use IMGfromGPX (JaVaWa) to transfer a track recorded with a gps or drawn with Mapsource, GoogleEarth or whatever. Some expermenting and use a map id that is not used in your system. This creates an .img map
Install this map with JaVaWa GMTK or install.cmd into your PC.
Now with Mapsource create a gmapsupp.img and install in gps.
In gps activate both the the new trackmap and the background map and you should see the track over the background map.
This will work for all garmin gps models as far as I know.

Other forum members maybe can contribute with even smarter and smoother ways to do this, I seldom use this method myself since I have my old 276C that can use routes better than nuvis.