I ended up writing my own procedure, with shell scripts slightly simpler than the ones provided by tshering:
https://anarc.at/hardware/tablet/kobo-clara-hd/
Upside: you get the latest version of whatever syncthing is currently shipping without me or tshering having to rebuild a KoboRoot.tgz.
Downside: you need to manually copy scripts around and generally, you need to know your way around a bit more.
Bonus: other cool hacks collected from elsewhere in one page.
