Sorry for the double post, but I think using the lumbar support pump/valve block from another car attached to the Tesla bladders might be the cleanest path here. The one I have in mind is the BMW F30 piece, but there may be other acceptable ones out there.
The BMW switch works similarly to the Tesla one in that the rocker connects outputs a different resistance to ground depending on which direction is pressed. I imagine the actual resistances are different than the Tesla switch, but that should be easy to work around. Unlike Tesla however, the valve body / motor electronics evaluate the difference resistances directly, rather than going through a body module and communicating over the LIN bus . So it really should just be a matter of connecting up power, ground and the switch.
The BMW valve body and pump look like they'd mount quite similarly to the Tesla bits (in fact the actual bladders themselves look very similar too, but would probably be best to just use the tesla bladders).