Shuffle and cut the deck. You can even let the spectator do so.
Spread the cards and have the spectator choose and memorize one.
Once memorized, ask him to place it on top of the deck.
Using some nifty shuffling methods, "control" the top card all the way to the bottom of the deck. This can be done through overhand shuffling the easiest.
Glide force the bottom card back by pulling it an inch towards you.
Ask the spectator to pick any number. Whatever number he says, deal that many cards from the bottom, making sure to keep the chosen card held back an inch.
Remind him that he shuffled the deck, you shuffled once the card was placed back and that he named a random number. Once he remembers that, explain you will deal the next card and it will be his. Push the bottom card forward and deal it down, revealing it to be his.