Boot the RELEASE iso from grub2 ?

[Trois Six]

Hi,

I would like to test the LVM capabilities of DragonFlyBSD. My goal is to 
have if possible a double boot (Linux / Dfly) with LVM only. To test 
that configuration I would like to start a boot of the RELEASE iso from 
grub with a loopback device.

At the moment I have a running Debian setup on my PC with grub2.

I downloaded the RELEASE iso and put it on my /boot

I tried the following configuration on grub2 :

. ..
menuentry "DragonFlyBSD 2.8.2 i386" {
        insmod lvm
        insmod part_msdos
        insmod ext2
        set root='(TroisSixNet_vg0-boot)'
        search --no-floppy --fs-uuid --set 
c634150e-a14c-4d5b-b854-dc1f65a8212e
        insmod iso9660
        insmod bsd
        loopback loop /dfly-i386-2.8.2_REL.iso
        kfreebsd (loop)/boot/kernel.SMP/kernel
        set FreeBSD.vfs.root.mountfrom=cd9660:acd0
}
. ..

It boots but it doesn't find the root device. What am I supposed to use 
in that case ? I know that I could boot from an usb key but I think that 
booting from grub like this is very convenient.

Regards,

Trois Six