If need be: partnew can be used to create the partition entry. A grub4dos batch to create a UEFI image fake partiton.
we need then to feed the (hopefully valid) result into a small batch similar to the partnew command in grub4dos, I believe that for isohybrid compatibility only the "Magic Bytes" need to be added (besides the partition entry
However grub4dos dosn't boot at UEFI mode. A BIOS boot would be necessary.
I would prefer a windows approach.
To investigate a isohybrided ubuntu-14.10-desktop-amd64.iso, both MBR and GPT partitions
The file ubuntu.iso hexedited, gpt deleted, MBR boot code deleted.
loopback loop /ubuntu.iso
(loop) (loop,msdos2) (loop,apple2) (loop,apple2)
One non active partiton entry and "Magic Bytes" exist still:
loopback mounts the EFI image at (loop,msdos2).