Thanks for helping out with this. If the request is still open in the tracker, it's very likely that it still hasn't been implemented.
It would be great, if you could offer a patch for this. However, I currently don't know the code and don't have the time to look at it, so I'm afraid, I can't be of big help for you.
You could also try to jfreechart-developers Mailinglist
to get some help.
Implementing the feature via 1. or 2. is up to you. If the user could choose, it would be even better
BTW, two other students also just offered to fix some bug as part of their studies via the dev-mailinglist.