I have always used cutter comp on 2 1/2 axis work, mainly because the work I've done required very high tolerences and it is the best way to tune the program. I most often have used the diameter or radius of the tool, varying the number as needed to get the dimn. with the program definded to the print dimn. Maybe I'm just old school.
I have heard of using a "0" call out as the offset, running the cutter path in its programmed offset path with the g41 or g42 callouts and if the, need arises, use a minus or plus as necessary to correct cut.
In the the old 2 1/2 axis CAM I have, it has this option so I assume that VM had it but I have not as yet found it.
Steve