EMC2 is great! Next project: CAM ??

If you don't have home switches, and if the axis limits have enough space in the negative directions, then you can do exactly what you describe, setting zero with the "home" button.
In effect, that means you are machining in the G53 (machine) coordinate system. (actually, you are probably in G54 system, but that is probably identical to G53 at the moment).

You might find you have a problem if you do use "touch-off" at any point. That offsets the working system from the machine system. Once there is an offset you will find that "home" no longer zeros the onscreen system, it will set it to be equal to the offset.

If you don't have homing set up in the ini file EMC sets the current location to the Axis 0. The back plot will move but the machine will not when you press home. I used to think like you are thinking but have come away from the Dark Side and now follow what I and Andy suggested on machines without homing switches and use the actual G54 coordinate system to touch off the material however you want.

John