Tell me more about the mechanism. The switch's middle detent is your only way of stopping the motor currently when it's travel is fully extended? I have (5) skylights that operate with 24 volt dc and from what I can gather sense a current spike to stop the motor. I at first used a timer for opening and a reed switch for sensing closed status. When the Velux stuff started popping up on Ebay I finally aquired all I needed to go propriatary. I think you can devise a self-supervising relay reversing scheme to make sure that you don't short your AC. I remember seeing a circuit with dual contactors that made it physically impossible for the motor to see both forward and reverse phasing at the same time. Would a mechanical clutch be feasible so a simple timer would work for motor stop?