"The other thing you ask for, loopback chaining, is not
possible, because grub’s loopback code will not be ac-
cessible from within the chained-to bootloader. Sorry.
You could achieve something similar with MEMDISK, but
only for relatively small images."
Taken from http://michael-prokop.at/blog/2009/05/25/b...-iso-via-grub2/
looks like it's not do-able =(