That is indeed an interestin' setup- I thought at first ye were using one of them combined fancy twist shifters 'til i saw the gripshift writing and the thumbshifter.
Ye make me feel rightly guilty for sitting on my arse saying "oooh, its a bit wet outside...."
I too am curious how you grab the other grip. I keep having the hook vision in my head. I would be thinking of some kind of SPD or something, or am I thinking too much? :?