Got to
RAM-Mount-UK.com.
Click on Customer Galleries, Bike Mount Reviews, BMW
And you'll see various set ups using RAM parts.
You maybe able to fit a Touratech bracket onto a RAM mount - you certainly could with the ones for Garmin V's and SPIII's.
Touratech mount normally fits on the cross bar of your bike - so only one position really, down low.
RAM mounts enable you to fit/position the GPS exactly where you want it to be.
A combination of both can also be achieved, as some Touratech mounts are lockable, RAM/Garmin ones aren't.
I'd wedge out and get a Migsel mount
Look at review Quest 5 for pics of the Quest mounted and review 6 for more on Migsels mount.
HTH
Jon