Nine cards are laid out, face down, in three rows of three. (eh: You can have them choose a card by the method in Find The Card The Easy Way.) Once a card has been selected, have someone call your assistant back in.
When the assistant returns, you are holding the rest of the deck in your left hand. Your thumb will represent which card was chosen. Example: if the spectator chooses the card in the middle, when the assistant returned, your thumb would be directly in the middle of the deck. You will have to do this once for the row the card is in, and again for the column.
The trick is to be VERY DISCRETE when holding the deck. Shuffle the deck a little so as not to draw attention to yourself. Keep a serious look on your face, and stare at the assistant, as if you actually had ESP. Let your assistant reveal the chosen card.