XYZ Adjust Z, Preserve Focus

I'd love to be able to "preserve" a focus, but adjust the stored Z value.

IE: I make a focus in Pan/Tilt, and save it to a preset with whatever the XYZ value happens to be when I save it. I then end up needing to swap to a different fixture, but want to preserve the focus Z height of approx. 6' for a person. I'd love to be able to adjust the Z axis so that X and Y auto adjust and the overall output to the light remains the same.