Hi jay, have you had a chance to give that a shot? I have a similar setup in my apartment (O, G, Y, and R wires only), but I’d like to confirm that it would work before I buy one of these if I can. For what it’s worth, I think the diode idea will work as long as the breakdown voltage is higher than 24V. An alternative I can think of would be to modify the firmware to make the “unused” W wire act like the “O” wire instead, though that’s obviously not ideal either.