I think the trick to making this look magical is time misdirection and how the deck is gripped. The way I personally do it is to start by gripping the deck face-up in mechanic's grip. I am standing. The selected card has been controlled to the top of the deck (i.e., it is face down on the actual top of the deck, but it is actually the bottom card of the face-up deck, if that makes sense.). When no one is paying particular attention to my hands, in other words, not immediately after a control is executed, and as I address a comment or question to the spectator(s), the palming of the card is accomplished, by holding the deck in biddle grip with the hand that will palm the card and sliding the card over from underneath with the fingers of the other hand.
The face-up deck is immediately re-gripped from above and held for a few moments with the hand that is palming the card. The naturally curved hand and the fact that it is holding the deck, make it appear that it could not possibly be holding a card. The guilty hand then drops casually to my side, while the other hand takes and holds the deck face outward toward the spectators. After calling attention to the face up card on the bottom of the deck, and asking if it their selection (and they say no), the guilty hand is brought up and with an upward magical waving motion, depositing the selection on the deck, opening the fingers wide after the card is deposited, and making sure the card is flush and square with the other cards. It appears you just waved your hand over the wrong card and changed it into the selection. Just my way of doing it - I am sure there are a number of good ways...
