Neil, you have some sort of Mac, right?
Could you (or someone with a mac) try if you can get this working?
http://routegadget.net/gps/QDRoute.zip
Install some stuff first as readme tells. Then tun the script, app first select gpx file, then a map image, drag blue points, add new ones by pressing with mouse button over 1 sec, and remove edit points by pressing over 3 seconds. Save as jpg/png.