Waiting for operator.

Hi,
I'm a long term cnc user and have done a lot of cnc repair, but am just becoming familiar with the amazing power of EMC.
One of the first projects that I am contemplating would be rather non-standard. The easiest way to envision it is to imagine a normal knee mill with X and Y conrolled. but with manual Z.
Ignoring safety issues, since this isn't really what I want to do, but imagine the controller positioning X and Y, but then an M code which would wait for the operator to move Z which would close a switch,
and then the program would continue. Most M codes just output and go, or with set delay, but here I'd want to wait for input, and then go.
This doesn't look too hard, and if I look hard at the probing routines, I might be able to figure it out, but other suggestions of examples would be appreciated.

The further refinement which I think would be much harder to implement is as follows:
Controller positions X and Y, operator manually moves Z, and when it is within a tolerance zone "near in hal parlance" of a programmable value, the program would continue.
I guess one way would be to figure out how to get EMC to not error out for excess following error on the Z axis, and pretend it was controlled. I'd obviously need the encoder input for Z, so I guess that as far as EMC is concerned, I'd have a 3 joint machine already.

Any ideas on an elegant way to accomplish the second scenario?
Thanks. I look forward to actually getting EMC to move some hardware.
lm

Yes, perfect.
Thanks for the nudge in the right direction.
Pays to read the documentation all the way to the end. I've not seen that M code before.
lm