From my unfinished testing, when a chromebook is enterprised enrolled, it sets a few flags in fw to prevent dev-mode and such, and checks the serial number on set-up to confirm enrollment. This is assumed because reflashing the firmware externally with a copy from the shellball is no longer doing any of the enrollment stuff.
I was supposed to confirm this theory by putting the enrolled serial on another device and see how it reacts, but im lazy.
The most common route is to get a raspberry pi. They're cheap ($35 for the more popular model b, or about $20 for the basic model a), and useful for a lot more than this task. If you have the money for one, and want to invest in something with countless other uses, grab one.
You can also pick up a beaglebone black. Similar to the pi, but with a (in my opinion) much better cpu and other hardware. More pricy than a pi, and not as popular, but still some pretty cool hardware.
Or you can go the cheap-ass way and pick up a chinese arduino clone and usb-serial adapter. On ebay I got an ftdi adapter for about $3, and 2 arduino pro mini closes for around $4. Requires a lot more work than the above options, but less pricy. Use this for a basic idea of what goes where, and where to get the ardiono software. I soldered the pin headers on the ardiono, and i replaced the headers on the ftdi with wires with female jumper connectors. Using female-female jumper wires would have been much more simple. You do want an ftdi and not a prolific or something since the ftdi can do much faster non-standard speeds. A prolific would also do the job if you have one laying around, but flashing will take like 20x longer
You also really want a soic-8 clip. The ones from pomona cost like $20, so its a little pricy. You can do this without one, but do you really want to solder tiny wires onto the small chip, or just clip onto it? (i flashed my x200 without a clip since it uses a soic-16 chip. It worked, but I spent more time soldering than flashing. You can also test your luck with those $6 chinese clips, but I have yet to hear anything good about them.
step 1: get your programmer set up. I'd write some info about that, but the flashrom wiki has plenty.
step 2: get the shellball rom and add a hwid to it. link or linky
step 3: open your chromebook. If you are lucky, you'll find a nice guide here: https://www.chromium.org/chromium-os/developer-information-for-chrome-os-devices/. If not, good luck. I did this to a c200, and it wasn't too hard. Just unscrew the bottom screws, remove the bottom, unplug everything from the mobo and unscrew it, and it was like the only soic-8 chip on the side with the cpu. I also had to flash an acer c710 once or twice, and it was more involved.
step 4: clip on
step 5: run flashrom and flash
Were you expecting a detailed step by steb guide walking any dummy through the proccess? I aint got time fo dat. And there's too many chrome devices for a generic guide to be good enough. If you have any tips to improve this guide without ruining the generic-ness, email me or something.
wait, you scrolled all the way to the bottom of the page? congradulations! you won a special prize. apparently theres another way to do this that while still requires firmware changes, doesn't involve external flashing. follow this link for the original post, or this one for my copypaste in case it gets taken down