The simplest database insert that worked as of the 4.4 firmware was:
INSERT INTO user (UserID,UserKey) VALUES('1','');
(Note, that last value is two single ' with nothing in between them, not a double quote (")
Once you have a database with a blank user, you can just copy that into the .kobo directory (and restart). I've been using the same database file for every new generation of device and firmware. Much simpler and easier than registration and sync, fake or not.
Anyone who wants it is welcome to copy the database file I've been using:
(I've attached a zipped copy this message, as well as a link to zippy)
https://www66.zippyshare.com/v/g56DQJzy/file.html