Just a suggestion - what if a switch was used for the up and down buttons that was similar to the VTR rotary dial? I am thinking more like a thumb wheel that could rotate up or down (not continuous rotation) and this thumb wheel could be near the fire button.
@devdev that will require different electronics, the DNA30 (which seems to be internationally the most popular) only use up /down switches and not a rotary potentiometer like the VTR.