Just in case anyone else wants to try doing this here was the solution I found and I like a lot :
http://www.motoreva.com/ You can arrange the Tomtom so it sits just above the ignition lock on the tank.. or higher if you prefer, keeping it easily visible, a help as it sometimes forgets to let you know which lane to peel off into.
It also meant I got to change the steering heade nut some A*****e ripped up when tightening the steering head bearings after fitting them.
Threaded Mode