@Kiwidude: Thanks for your explanation. I see your points. I had hoped I asked for something simple, but apparently I did not. You are right that it would be better to get the bug resolved rather than work around it. But then, I am afraid that requests sent to those developers may end up in some sort of bottomless pit, whereas you actually respond to requests (even though it is a 'no' this time).
Well, I'll give it a try anyway, and in the meantime use alternative solutions (edit the ePub manually / use another reader program / convert ePubs to another format).