Dear lstein,
I am looking for the same thing, a way to have a boot possibility from an external usb (or firewire) hard disk.
In my case it is necessary to modify the boot disk because my laptop computer doent support usb booting.
If it is possible to you send me instructions for hao can do that, or keep me informed when your iso is avaiable somewhere and I can download it

Best Regards
Mike Kranidis