Finally worked up the courage to try this today and ended up with a fresh phone (not what I wanted).
Here's what I did;
put phone in fastboot mode (by pressing vol up, vol down and power)
fastboot devices (to make sure it could see it)
fastboot oem unlock
fastboot flash system system.img (from Kitkat 4.4.2, same OS I was running before this crap started)
fastboot oem lock
Then I got to pick a language and start the setup, just like when it came out of the box (minus all my apps, data and pics)...