Richard,
I literally wake up in the middle of the night thinking about this exact subject, and from all that I understand about this, you can not re linearize the Piezography .quad files.
So I was having the same thoughts about 6 years ago and knew there must be a way to do this because Jon Cone provides this as a service. After many months of wracking my brain and experimenting, I had a light bulb moment and realised the solution was staring me in the face all the time - you simply print and measure the linearization strip and that creates a response curve for your printer+ink+paper. Then you do a reverse lookup from that curve back the the quad file values for the linear steps you want to use.
So to give a simple example, if hypothetically you want to linearize at Lab Dmin,10,20,30,40,50,60,70,80,90,Dmax
you simply extract from the quad file the values that give you these Lab values on your response curve.
The only requirement is that original response curve has to be continuously increasing otherwise you can get duplicate values that this approach cannot resolve. But that's easy to avoid with a reasonable step width.
It works great and I was able to use linearization steps from 21 to 128+ with ease. 128+ is a special case and requires a consistent paper surface and the average of several sets of readings, which in turn is only practical with a sheet reading spectro.
To do this in practise you need to set up a spreadsheet to do the heavy lifting of searching for the values and filling in the gaps between the linearization points etc. I created one for my own use and shared a version with a few others to test - which all worked great. I was planning to develop a web based service to do this cheaply for others, but I got waylaid by other more financially pressing projects. I've been thinking for the last year or two that I should share more widely the work I did, so others can use it.
When I've got some time over Christmas I will share the spreadsheets and some simple instructions.
Cheers,
Mike