I ended up getting myself a programmer and dumped the first chip. The system has dual-chips, with the second one containing just the BIOS region. The second is a WSON so I would rather not try to desolder/solder it.
I extracted the BIOS region from a Dell firmware update and glued it to the dumped file as a placeholder. Without it, MFIT can’t build and UEFITool gives an error.
I opened the file in MFIT and enabled the AMT settings, then built the image. I plan on flashing this tomorrow with flashrom, using the file descriptor flag to only flash the ME region.
Am I missing anything? As far as I know, this was the way to do it for CSME versions <16.