So, we've finally thrown the lever on this. Doing a fresh build, with a recent or self-built version of Chromium for Chromium OS should allow you to use this feature. It'll only look a little different, but really the main plus is that you can pick wifi networks from the login screen. We'll be working on more speed tweaks and snazzy login UI in the coming weeks.
The main known issue right now is that if you log in with the backdoor account you created at build-time, and the screen locker kicks in, you'll be locked out and have to reboot. I have a quick fix that works, but it'll require a change or two on the buildbots as well. If you log in with a google account, it'll work fine. And, since you no longer need to log in to configure network connectivity...why use the localaccount anymore ;-)