I would be very grateful if someone (KevinShort?) could PM me a download link (and any parameters necessary for dd or other flashing methods required): so far I did not get one.
To answer some questions:
1. The battery was fully charged when I disconnected the Kobo from the computer.
2. Before opening the device I contacted Kobo's technical support, which made me attempt a factory reset. Unfortunately, the device did not respond at all to the procedure and in the end I was told to ship the Kobo back.
3. I tried what I did as I read somewhere else on the forum someone describing the partition structure (2 linux formatted partitions for system data + 1 fat partition for user data) and figured at that point I had nothing to lose by cracking the thing open and trying to remove the offending file myself from a PC.
Thanks everyone for all the help so far.