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.

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?

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.