If the playback manager makes a good use of provided foreign PIDs, than the cleanest approach would be to rewrite the widget, but I still have to test it and I don't know if I'd have enough time for another project. Doing what the stock player does wouldn't play well with "Do nothing" set as the exit action or Nicolai's widget, but fortunately the stock widget appears to send different things on D-Bus when there's playback going on, so I'll try to make a use of that.
One thing I noticed today was that settings for the headset are only updated when the headset is removed and then reinserted.
Found a strange thing too, dont know if its just me. Well, when I add new albums the thumbnails isnt imported in the All Album view. But if I play the album the thumbnail is there.