I don't have my installation in front of me and I am not allowed to post links so...
Use Garmins installer to install the map. The map is now in GMAP-format at
%allusersprofile%\Application Data\GARMIN\Maps
Delete all ".dem"-files in the underlying folders. (search for ".dem" in subfolders)
Run "MapReverseConverter" and then uninstall the map. You will now have a copy of the locked map in IMG-format usable in Mapsource 6.13.7.
Run "All.bat" from "Garmin Unlocker" and the map will be unlocked.