I got this info from Tomtom's website:
To select the your HP iPAQ 6510 or 6515's internal GPS receiver using Navigator 6, see following instructions:
1. Open the File Explorer and browse to the folder Navigator.
2. Delete the file navigator (be sure not to delete the file TomTom Navigator or you will need to reinstall the application).
3. Start TomTom NAVIGATOR 6.
4. When prompted, select Other NMEA GPS receiver.
5. Set the GPS baud rate to 4800.
6. Select Internal AGPS NMEA.
This is the method to detect the internal GPS on an HP 6515/6915. I suppose there should be some workaround for us too.