Got it to work, but very difficult.
In order to patch the AppleFileSystemDriver I had to use nano -w in terminal. The directions on these boards are not very newb friendly. Anyhow, after numerous hours of trying it finally booted. Pretty cool to have osx externally and not have to crack open your Atv. The only problem now is getting a keyboard and mouse. I tried my usb hub but since it was old and 1.0 it didn't load the drive. My guess is it'll need a USB 2.0 hub to load the drive and be able to use a keyboard and mouse. Either way though the USB drive will never mount on your Mac anymore after changing partition types, so this won't make a practical solution for putting files into you Atv, since you won't be able to put files into your external drive. If anybody is looking for the boot.efi file just get the Atv.dmg from bittorent or whatever and mount it. The file will be in the mounted drive.