The solution does exactly what the OP wanted.1. I have knoppix on my usb to fix PCs ...
2. I do not always use the same PC and/or laptops since clients vary ..
..
4. .. if I could have a knoppix-data.img on every user's hard drive partition ..
.. Then once I boot knoppix from my usb, ..
.. looking for the img file and if found, it is used as the overlay file.