Also, if you do go the ShiftMate with a 10spd shifter, it might be better to fit it near the shifter rather than the derailleur, in order maximise signal-to-noise in the system; the cable pull per 10spd shift is pretty damn small.

Of course, you'd miss out on the removal of a bit of friction from the RD loop the ShiftMate provides, and it'd look a bit weird, so try it the normal way first.