In MMjoySetup, tab Joystick Axes (Spec.Functions), use "Axes to button" - bellow left.

Choose the button number, the axis that will press this button, and the % range you want that axis press this button, example: 0% to 5%, then "Save settings to device".

For this "Special Functions" you can use buttons from #1 to #32. Above # 32 only don't support "Special Functions".