Errrr..... has anyone had any experience with wiring home switches to an X axis thats driven with two steppers ?

in mach setup documentation it recomends putting a homing switch on each of the two x-axis drives to correct for lost steps and racking which im getting plenty of as im in the tuning stages of my setup... i only have enough inputs for 3 homing switches and an e-stop on my driver board

how do i conjure up a forth input ???????