@Fernando-Gietz So lets think about it a bit. in a way you want to tell the pxe booting client (in iPXE) don’t boot of the normal boot loader, but boot from a different partition (lets use /dev/sda6 for discussion). By default sanboot will boot from the first hard drive, and uefi will boot via refind.
Grub can boot uefi. I don’t know if grub distributed with FOG can boot uefi.
If you set the exit mode for a host to Grub first hard drive the iPXE menu is created this way:
chain -ar ${boot-url}/service/ipxe/grub.exe --config-file="rootnoverify (hd0);chainloader +1" || goto MENU
I’m wondering if someone could repurpose the setting rootnoverify (hd0);chainloader +1 to actually load /dev/sda6?
The other challenge is that grub.exe is probably a bios mode application where we would want to use grub.efi for uefi.
Again this is just me thinking out loud about the issue.