BTW - there is a lot of useful information in the original, now archived, thread (https://h30434.www3.hp.com/t5/Desktops-Archive-Read-Only/z820-e5-2600-v2-ivy-bridge-upgrade/m-p/5086052) but it also has some not so good information.
Referencing the post above with the YouTube video, the Z820 also has an SPI header along the lower right hand edge. I tried using that rather than removing the chip but it did not work for me.
If you run Flashrom, as I did, in the Z820 to be upgraded using the Linux based SystemRescueCD live CD (http://www.system-rescue-cd.org/) you can read and save the BIOS contents. It is this read BIOS information that you will use to write back to the board once you have substituted the Boot Block with one that allows the V2 to boot (need a binary editor to do the substitution). Once you have the modified BIOS, save it on a USB drive, remove the board from the Z820 and pretty much follow the steps in the video.
The key is that you will be writing back the BIOS that the board had but with the substituted Boot Block. This keeps all the other important information in the BIOS intact. It has been done and works contrary to that in a prior post here.
Just for completeness ... photo of SPI location attched
