Just to be sure, the nubbin is this small black piece of plastic, right?
!Imgur: The magic of the Internet !:Imgur: The magic of the Internet
If so, yes, that is what I did 
I flipped the silicon cap and the nubbin is now touching the metal cap.
I found out that, at least on mine, the curve (dome) on the silicon cap needed to be pushed down to make pressure more evenly to avoid noise due to a single pressure point.
After trying several “normal” silicon buttons, with and without the original below them, it was that solution what helped.
Later I may try to take a photo if needed, as I don’t have the FW3A with me atm!