Mark, I don't know how much control the software you are using allows but one thought on conjuring up a second X home switch is to mount a single switch on the Z axis such that it 'makes' against an edge at the 'home' end of the table.

Drive the Z to the far left and you have a 'home' for the left X screw, drive the head to the right and you have a 'home' for the right screw. Not ideal for the final design perhaps but it certainly gives you some way of tracking the racking while messing around :)