Interesting product (the TMAT switch). I think something can definitely be made to work but the standard threadless version won't be it. What I see as the best possibility for integrating a switch is to have a portion of the innicycle steerer tube extending above the stem and using a magnetic switch (like the prototype quill version) in that location. The wedge will need to be drilled to pass wiring through and care will need to be taken to not interfere with the top cap as it protrudes into the steerer quite a bit (reference the cross section image I posted way back in this thread).

While this isn't necessarily something I want to get into myself, I'm happy to consult and provide spare parts for modification as necessary to whoever decides to take this project on.