Actually, this is old stuff. There were a lot of cardboard cutouts in the crowd in The Natural - 1984.
“About 3,000 people were recruited to play extras in the stands — at the then-minimum wage of $3.35 an hour. Obviously, there still weren’t enough folks to fill the stadium. According to a contributor to Digital City Buffalo’s Movies bulletin board, “FN Burt, [a printing company] made cardboard people to be placed in the stadium during filming to cut back on the cost of extras.””
From here: http://espn.go.com/page2/s/closer/020918.html