I just replaced the butterfly-mechanism without removing the cup. It seems to be possible by stretching the new mechanism over from one side to the other (just like the video referred to earlier describes). However, the key travel appears to be less than with the original mechanism. I noticed that the original mechanism had 'G018' stated on the upper-left corner, whereas the replacement part has 'G019' on the same spot. I really hope that this worthless mechanism isn't applied in future MBs/MBPs.