Just throwing it out there so dont quote me if it dosnt work, just throwing it off the brain.
pull your pod of switches out of the door, flip them over and unhook your wires that you previously hooked up to them. get a flat head screw driver and pop the backing off ( very easy to break ) so be gentle. if you want your down button to dump your bag valve take the backing off the buttion itself. get a pair of wire snippers and cut the feed to the up button when pushed...it will either be saudered or a combo or a greeen and blue wire. either one can be cut to prevent any power running to that certian position. MAKE SURE you sauder the wire you cut, back over to the down button. doin this prevents the relay from switching out and the up button will be disabled.