ah in that case it's dead easy, hold the deck as you would for the glide. A ask the spec a question or ask them to think of something. While you've got eye contact, lift the deck slightly and at the same time turn your hand over. It only takes a second and shouldn't get spotted.
There is a move that is taught by Justin Miller in the Army of 52 DVD... I don't remember what it's called and I'm at work so I don't have my DVD handy... Basically you flip the deck over with your left index finger while in a mechanics grip....
While I have the technique down to a workable level, I have yet to try this in public and was wondering if anyone had any experience with this?