It's not exactly what I'm looking for, since I would like to include just certain forums, but it's a good hint anyways. I know there's a plugin that will dig into a page's sourcecode & just include a matching part of it, so I'll give it a try.
Yepp, I've got it. Guess I missed this because of the interface's i18n to german. The option would more appropriate be called "Abschnitt" rather than "Bereich" (which is more generic than the former).