Source the interior door looms and electric motors, plumb the wiring in the door. on the car interior loom there are 3 wires, 2 orange+white ones on the drivers side and a red. and 2 orange+white on the passenger side. link the orange/white wires from the drivers side the passenger side but don't cross them this is the + signal to the other side. snip the red wire on the interior loom stick 12v to the red wire leading into the door loom and hey presto! jobs a goodun both switches work on both passenger and drivers side.
i'll post up a photo of the wires on my old loom later before i converted to a 172 i had this done on my 1998 mk2 ph1