Two Joints for Z Axis

Hi I am retrofitting my Picomax found a 740mm gals scale in my spare parts box and I am wondering If I can use it to enhance my Z axis

This is my machine an the quill is controlled by a servo and has 400 mm of travel. And is the normal Z axis right now.
But I can Oslo Move the whole column 720mm but it has no scales at the moment. It is not controlledlike an cnc axis.
I have four limit switches which van be set by moving notches so I can move the column with four M codes to these preset positions.
But I can also move between the preset positions kind of free.
These M-Codes first unclamp the column and then Move the Column and then clamp it again.
My idea is to add the glas scales to the column, So I now exactly how much the Column moves and I don't have to re zero the Z axis after movement.
On the other hand I want only the quill to be sonsicered when checking for Z axis limits while checking the range of motion for cutting. Caus I can't move the column while cutting.
This way I can write one program for each tool and move the column between tool when needed without resetting the WCS.

Is there a way to set this up ind linuxcnc?

A dream would be to check the range of motion for one tool and then set the column height for cutting with the tool change. But I guess this is not possible. 

Thanks Patrick
 

Thanks.
Still need to wrap my head around it a bit.
I don't want to home the column, so I need a way to reset the encoder position on startup.
The column doesn't move, It is clamped, except when planing to move.
The rest sounds like it can be done with offset hal.

This way I can get the basic the current functions running without resetting my wcs.

Next step (Ok first the machine need to run, then the Column-Encoder) would be to find a way to move the column to a specific height without changing the brake amplifier to vfd. I might be a bit to slow in python.
But maybe could be done with wcomp and gcode and a bit dailing in. It doesn't need to be exact +- 1mm should be more than enough. But giving the speed in which the column moves I guess -+0,2mm should be possible.