HP Chromebook 11 Cannot Boot from USB with Arch Linux ARM

[unteer]

I have a HP Chromebook 11 G1 and have installed Arch Linux ARM using the Starkers script: https://github.com/starkers/archbook. I completed the installation by installing Arch directly onto the mmcbl0 device. Now I am interested in trying other distributions and have tried to boot from USB using the Ctrl+U at the developer mode scare screen. When I do that, I get a warning that the firmware is in read only mode.

From Arch Arm, how can I restore the firmware to read-write mode? Normally, I believe this is what the ChromeOS crossystem command is used for, but Arch Arm does not have crossystem. Should I compile crossystem for Arch Arm from the chromium repo?

Any help would be greatly appreciated. Thanks!