Modifying GPS Desired Track

Hey all,Has anyone ever done any work which relates to modifying the FS9 GPS DTK(Desired Track)? It seems to be "hard wired" to the course between the previous waypoint and the next waypoint. I have not been able to find any GPS var (assuming one even exists) which can modify the default track, although it can be read with (A:GPS WP DESIRED TRACK,xxx). I know many GPS systems can do this in a similar way to an OBS.Anyone?--Jon