Hi Rob,
The short answer is no, I'm as frustrated as you are!!
I use a Garmin Zumo 660 both on and off my bikes, and you can forget any suction mounting due to its size. On the bikes I use RAM ball mounts, so still thinking about dash board screw fixings to pick up on for a ball mount, but it's still on the drawing board..
For holidays, I mounted it in it's suction cradle and used plastic ties to loosely hold it onto the flat area ahead of the gear lever. This worked better than expected, but it's not in the zone for easy glancing. Better than getting wrong slotted in a busy French town, though!
An interesting topic..
