The reddit comments pointed out that there was a previous (unofficial) contest last year [0]. Manishearth had a fun solution with lots of ideas: [1].
[0] https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_ru...
[1] https://play.rust-lang.org/?gist=cadcbee43557e8e3bbe0&versio...