Not that they haven't thought about this: The cardinals are in "choir dress" during the voting, which has translucent lace sleeves under a short red cape, making sleight-of-hand tricks much harder.
Steichen's images--many of which you've likely seen in photography books (a young Gloria Swanson, mysterious and smoldering behind a black lace veil, or Charlie Chaplin goofing around with a cane and bowler hat)--don't appear particularly controversial.