up on the table. (eh: you spell the cards in order: ace, 2, 3, 4, 5, 6, 7, 8, 9, 10, j, q, k) your audience may realize that the cards must have been set up beforehand, but this only adds to the mystery - and you can treat it as a puzzle for them to try to figure out.
editor's note: to add to the mystery, don't use cards all of the same suit. a mixed group of suits makes it seem less like a "stacked" deck. 