linux - From GRUB2, boot an ISO in an LVM2 logical volume

tl;dr - Is it possible to boot from a .iso file that is located in an unencrypted lmv2 logical volume? How?

I'm trying to set this up in a VirtualBox VM before I do it for real with my laptop. I have the following set up:

• 4 gpt partitions
  
  
  
  • gpt1 - 2M ef02 bios boot
  
  
  • gpt2 - 5G unencrypted non-lvm, for misc data,iso's, etc.
  
  
  • gpt3 - 5G unencrypted lvm, for /boot,iso's, etc.
  
  
  • gpt4 - remaining, lvm, encrypted with dm-crypt/luks, for root,swap,home,etc.
  
  
  
  


• in gpt2, I have copies of current Arch and Xubuntu iso's


• in gpt3, I have an lvm2 lv with the same copies of the same iso's

I have the following working:

• in gpt4, functioning installs of Arch and Xubuntu (and would like to add other distro's in other logical volumes at some point)


• grub2 installed from Arch on /dev/sda


• using grub2's configfile command, can switch and boot from both distro's grub2 menu's


• can boot iso's from grub menu from non-lvm gpt2

What I would like to do is boot from the iso's in gpt3 lvm (and ultimately, not even have the non-lvm gpt2 partition at all).

My grub entry is:

menuentry "Xubuntu ISO" {
  set isofile="/xubuntu-12.04.1-desktop-amd64.iso"
  # from non-lvm
  loopback loop (hd0,gpt2)$isofile
  # from lvm
  #loopback loop (vgboot-iso)$isofile
  linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile noprompt noeject
  initrd (loop)/casper/initrd.lz
}

The 2 loopback lines point to 2 different copies of the same iso. I've verified at the grub command line that both loopback lines work.

When booting from the iso in the non-lvm partition, everything works fine.

When booting from the iso in the lvm partition, the boot starts, and eventually gets this error:

(initramfs) /scripts/casper-premount/20iso_scan: line 46: can't open /dev/sr0: No medium found

For the arch entry:

menuentry "Arch ISO" {
  set isofile="/archlinux-2012.09.07-dual.iso"
  loopback loop (hd0,gpt2)$isofile
  #loopback loop (vgboot-iso)$isofile
  linux (loop)/arch/boot/x86_64/vmlinuz archisolabel=ARCH_201209 img_dev=/dev/sda2 img_loop=$isofile earlymodules=loop
  initrd (loop)/arch/boot/x86_64/archiso.img
}

booting from gpt2 iso works, but I don't know what to change the "/dev/sda2" to for lvm boot.

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EDIT: Can this be done? For any current Linux distro's official .iso file? Fedora? Debian? openSUSE? CentOS?

Is this impossible? Or is it something no one has thought to try before?

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EDIT2: My bounty has long since expired, and after 9 months, I'm assuming this is simply not possible with any Linux distro. I'll leave the question open, but I'm doubtful there will be a working solution anytime in the near future.