Here's one from July 2013: https://www.watchuseek.com/f17/cleaning-white-g-shock-887208.html
It references these four threads, too -- the third one down is from February 2013:
It says "orange" in the title, but the cleaning tips are the same: https://www.watchuseek.com/f17/how-clean-orange-g-821400.html
I can't recall anybody finding -- and posting! -- any new methods since that July thread, though.