What control are you wanting - height and on/off - or is the "target" undulating.
You can search the forum - this question has come up before - and, I think, been answered.
If you look in Config/Ports and Pins/Mill Options you will see a box refering to THC which I think is Torch Height Control. THis allows you (I think) to alter the height of the Z axis whilst "on the move".
I don't know for sure, becasue I don't use the feature.