Bicycle Invisible Deck Only

Have a spectator remove a card from an imaginary deck then replace it face down in the pack. Now you remove a real pack from your pocket, spread the cards and there is one card face down. Unbelievably, it is their selected card. No forces. Any card they name will be face down in the pack.  Note:  Bicycle deck is opened, magically treated and sent to you.  (You can't do the trick if we don't  apply the magic to the cards first.)