For the impatient:
http://zhuoweizhang.net/Arctic.apk
Basically, this uses the vulnerability discovered by the Android Security Squad (
http://blog.sina.com.cn/s/blog_be6dacae0101bksm.html) to replace a system package - in this case, the Dark Knight status bar service that doesn't appear to be used anywhere.
Other root methods, such as Cydia Impactor, can also take advantage of this bug (which isn't patched on the Arc, unlike the first master key bug), however, they require a connection over USB to operate. Arctic uses the tablet's built-in factory test code to install su.
All credits go to the Android Security Squad and Saurik for finding and describing the bug, and to Chainfire for his SuperSU application included in the install.
To use, install the APK (make sure to enable installation from unknown sources - you might also need to disable app verification, although I didn't need to), and launch Arctic.
Another installation screen for Kobo Status Bar Service should pop up.
Agree and install, and after the install completes, you should have root.
Reboot if SuperSU doesn't show up. (If it still doesn't show up, try installing it from Google Play)
Source code:
https://github.com/zhuowei/arctic