Anything relating to in-game stuf means setting up MAME rather than MAMEWAH.
Goto a command prompt,
Navigate to your MAME folder - eg 'cd\mame',
Type 'mame -cc' or 'fastmame -cc' or whatever,
Type 'edit mame.ini' or 'edit fastmame.ini,
Find that part that says 'mouse 0',
Replace with 'mouse 1',
Go 'File' > 'Exit' and save changes.
Mouse input should now work for all trackball/spinner games.