I’m no real dev, but it seems MusicBrainz provides libraries for “easy” integration into third parties apps.
For example I stumbled on http://wiki.musicbrainz.org/PythonMusicBrainz2
Another maybe useful pointer (may be outdated): http://musicbrainz.org/development/index.html
Sorry I can’t provide more help Florian.
I know it’s a big piece of work, but that would be way cooler & cleaner than the MB web service file (.src), that moreover doesn’t write the musicbrainz-specific tags like MUSICBRAINZ ARTIST ID, etc., which make for easy later updating of the tags.