The people that are oblivious to taking up the whole moving walkway are the same ones impeding auto traffic in the fast lane when the lanes are open to the right. I usually just say "excuse me" or "on your left/right" loud enough for them to get the hint.

More moving walkways should be designed like the ones at DEN, more than one in each direction and wide enough that there is room enough to easily get around those standing on the side.