@TotallyFred, I guess that would be theoretically possible.
You would need to start with the machine unpowered, because otherwise the steppers are holding the axes in place and you can't slide them around manually. The Z axis requires some force to move since it is a leadscrew. Carbide Motion would need to know that you are starting from a desired "zero" position and count steps while it homes the axes, then back-fill for the Program Zero location.
I've not encountered a control software that does that, so maybe the Carbide guys can be innovators!
Even when steppers are unpowered, they have natural detents of step position that you can feel when you turn the shaft. So the manually-placed position would be only close as the closest motor detent. When steppers power up they default to a standard configuration of coils powered (I think usually both coils powered +) which might not correspond to the unpowered detent position. So the starting point would only be approximate, which for some workpieces would not be a problem. But it would not be accurate to the resolution of the Carbide Motion microstepping.
when I'm setting the axes, especially Z, I position the cutter to the lowest possible step (.01mm) using a piece of cigarette paper as a feeler gauge. Cigarette paper is typically .001" (.03mm) thick, so when the cutter is pinching the paper against the workpiece/stock I figure the cutter is actually touching the stock. That is the type of accuracy I typically work to. The move-and-power-on would likely be 10x or more worse in position accuracy than that.