This is probably a little too late for F-8. However, with F-8 installing on an
external usb disk is a breeze, maybe some words can be added to the install
guide that this is possible without extra effort. Plugging in the drive and
selecting it for installation is all it takes. Anaconda can also safely write
the GRUB bootloader on the external disk (I've tried it twice).
I think we note that you can install to any drive that's listed in the menu.
I'm not sure that pointing out external USB drives is a big win, because there
are many other external disks that also share this status -- RAID, iSCSI, etc.