^ it would be great to have more USB posts on the ATV, but from the sounds of it, to hack it to boot from USB device you also need a keyboard

"Booting from USB requires booting the Apple TV as nromal then holding ‘menu’ and ‘-’ keys on the remote to initiate a restore boot. From there it takes a bit of timing, Turbo explains, “If I hold down menu and - from poweron until the first screen flash, I believe that it does the equivalent of cmd-opt-p-r. I only got it to boot from USB by releasing it at that point, then hitting it again just before the screen flashes on the second reset.”