As is most often the case after banging one's head into the wall for a few hours and making no progress, then you humble yourself to ask for help... and suddenly the light bulb goes on!
I was trying to look for an answer working with the control, but with how it formats numbers for display I couldn't ride a wave for a solution.
so I stuck a crowbar into the control and extended it:
public class RRNumericUpDown :RadNumericUpDown
public override string FormatDisplay()
if (this.Value == 0.0d)
Hope this helps others looking for a similar solution.