subreptitious - A calculated misrepresentation through concealment of the facts.
arreptitious - Snatched away; seized or possessed, as a demoniac; raving; mad; crack-brained.
irreptitious - Characterized by creeping in or having crept in, esp. into a text.
I don't think I'm going to get much use out of these, especially irreptitious, but I do kind of like arreptitious. What scurrilous ratbag among us hasn't surreptitiously hatched an arreptitious plan?
Sounds kind of like Wile E. Coyote, dunnit?