My method is not exactly what you have asked but is close.
I set all tool tips to 0.0 on the table.
You then measure or calculate the height to the top (or bottom) of your workpiece from the table.
Eg my 4th axis is 6.5 to center
my vise is 2.875 to the base + parallel + Mat thickness.
Face of 3 jaw chuck 3.937
My 4th axis is G58
Vise is G54 (axis is XY 0)
3 jaw is g55 (back jaw and work stop = 0)
Sometimes I need to pick up 1 edge for my fixture offset but frequently I need to pick up nothing.
I do not use Z offsets for the fixture. Simply because I don't know how it will work, I have never had time to piss around figuring it out (if it is even doable?) and what I do works real good anyway.
I do most of my programming in CAM and offset the regions or model above Z zero to correspond with the fixture height on the machine.
Eg If the top of my material is 5" above table and I am cutting a 1" deep slot my tool will be programmed at H(tool number)Z4.0
IF I am required to pick up or remachine a precision component I will still do a custom setup (indicate the part itself and set tools to the part itself) to ensure that my setup is the best it can be.