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.