For anyone who wants to try, here's an open-source tool for editing Sqllite databases:
http://sqlitebrowser.sourceforge.net/
But I feel it's only fair to note that you can probably render your Kobo totally unuseable if you screw up the database on it. You should back it up before making any changes to it yourself.
I haven't tried this myself, although I would like to reverse-engineer the thing a little, just out of curiosity.