Comment 5 for bug 94204

It is already possible with the "iso-scan/filename" cheatcode. Here is an example grub2 menu entry:

menuentry "Ubuntu" {
 loopback loop /boot/isos/ubuntu.iso
 linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=/boot/isos/ubuntu.iso quiet splash noprompt --
 initrd (loop)/casper/initrd.gz
}