You should be able to use Screen4 to add a button to do this, I have just looked at the Mach2 screenset and the button for multipass is a button with VB script in it. If you add a button to Mach3 screenset (1024.set) you can choose to have it as a VB button and save it. Then when you go into Mach you should see the button you have created, go to the "Operator" tab then down to "Edit Button script". The new button should now be flashing, click on it and paste the the text below. Test it out with care as I have not tried it. You may also want to add the DROs that are present in the Mach2 screen.
Hood
REM Context 10002
repeats = Question ("How many iterations?")
depth = Question ("Maximum depth in first pass?")
perpass = Question ("Amount to drop on each pass?")
SetOEMDro 80, depth
SetOEMDro 78, repeats
SetOEMDro 79, perpass
DoOEMButton 218
Message "Press Cycle/Start to Begin"