So I've enabled dev mode and issued the command from root to enable usb boot via the developer console(ctrl-alt-f2(->)). "enable_dev_usb_boot". Says it was successful and that Ctrl-U will boot the self signed image. It does not.
I've tried the ASUS Chromebook flip image from 9/1 and 9/3. Ctrl-U just gives me a beep.
Any help would be appreciated.

NOTE: other threads talk about going to Ctrl-Alt-t to get a terminal window under chromeos, and issuing "sudo cgpt repair /dev/sda". I get a warning about the Primary and Secondary GPT header, saying it's invalid.