Hi,
without home switches Mach can 'home in place' So what you do is jog to a specific location, maybe bottom right corner with the
Z axis uppermost and then hit 'Ref All Home' and Mach will treat it current location as its home and reference the axes.
This method is as repeatable as you are accurate about jogging to the exact same location at the start of each Mach session.
Never likely to be as good as good quality home switches but....
Craig