I do believe that it is not possible for firmware to help you out there, what you need to do is use an xbox, flashfxp, and evo-x to copy it to your pc.
There is a tutorial on how to do that here:
http://www.xbox-scene.com/articles/iso-backup-guide.php
wait, scratch that, look at the sticky...I think you can, the link I provided has links to firmware sites if you need them