brunokc:
I would make it as simple as I could, so there were no extra buttons.
I've worked on many machines where the engineer cut the hardware to the bone. That's okay if the item still meets spec. The problem comes about a year later when we 'change the way we do business'. This generally involves logical gymnastics to accomplish something that would be a snap if there were another sensor/input available. Sometimes just adding another switch IS the simpler way.