The NiWumph MPU has a free play option.
Here is a link to the manual, this might not be the exact version of you board, but i believe the options are the same. You can get with Ni-Wumph and they can probably get you the info if this isn't correct.
http://www.ni-wumpf.com/Gottlieb/System%201/NiSystem1Mk2Manual.pdf