By looking at the wiring diagram, it appears that it might work as long as it don't send an error code to the ES control unit and cause it not to shift. You could try and see if it would work. I don't think it would hurt anything.
According to the wiring diagram, it's just a normal switch that's either open or closed. If it won't shift, then just switch it back. The only other thing that I can think of that would cause it not to work would be if the 450 has a reverse rev limiter, but I don't think it does. If it does have a reverse rev limiter, then the rev limiter will kick in at low RPM, even in forward gears.
After thinking a little more about it, Pain is probably right. It looks like one of those wires runs through the ECU and it might not be a good ideal to wire it straight through the switch. You might end up damaging the control unit. It would be a lot cheaper to just buy the reverse switch than it would be to replace the ECU. If it wouldn't have been an ES model, it wouldn't have been so bad.