Thanks. I was worried my handlebar mount (positioned on the clutch side) would interfere with the Ermax screen I mounted, but I checked it yesterday and it seems fine. I would still like to have the Zumo in the middle, but as you say, a handlebar mount may be the best solution.Drill a hole on the one you have? It's aluminium.
The OEM nut has a round machined part that fits into a recess on the top clamp and the steering head thread does not come up very far. It might be a bit difficult to find a suitable open nut.
I'd use the handlebar as a mounting point instead, just to keep things simpler.