Booting El Torito image from a partition table

[Emilio Lazo Zaia]

Hello

I have a bootable iso9660 hybrid image (mbr + eltorito) that was made 
with GRUB2 as its boot loader.

I would like to boot this ISO image from a partition table, i.e. boot 
into this ISO image but dumping the image to a partition on a GPT or MBR 
partition table, instead of dumping it to the partition table itself.

My disk contains only iso9660 images, one per partition. It boots with 
SYSLINUX -stored for example in the first partition- and using chain.c32 
module I can chainload into another partition's boot sector without 
issues if the ISO image boots with ISOLINUX.

All ISOLINUX images can become hybrid with isohybrid (or dumping 
isohdppx.bin to its beginning), but GRUB2 images can't become hybrid in 
the sense of booting also from a partition table; so it seems that 
boot_hybrid.img from GRUB2 does not support this scenario, only for 
images that were dumped to the beginning of a disk.

I did post a similar question in the SYSLINUX mailing list [1] asking if 
a patch or workaround is possible in SYSLINUX but the answer was negative.

There is a solution for this scenario or indeed the boot_hybrid.img from 
GRUB2 may be patched to support this?

Thanks
Emilio.

[1] http://www.syslinux.org/archives/2015-September/024086.html