Thanks for all the quick responses. I had thought about stacking the buttons, but as rdrast said, there is a potential for disaster. In my particular case the PB would trigger a signal which is still hardwired to the other PLC, so technically both would not need to have that input. But I thought I would ask for future reference.
The real kicker is that I am pretty sure this is easily done in proface HMI's, but then again, I am partial to that software anyway.
Look foward to hearing anyone elses ideas.