Enlist the aid of a friend or companion of your target spectator. Pull aside someone who appears outgoing and fun loving. Ask him to plant the card inside their friend's -- your mark's -- wallet. Swear this assistant to secrecy.
Employ a pickpocket or pickpocketing team. In advance of your performance, have a pickpocket take a spectator's wallet, load the card, return the wallet to the spectator's possession and point out the spectator to you.
Place a sleight-of-hand magician posing as a bouncer at the door to check guest identification. When a person presents his identification while it is still in his wallet, have the bouncer pretend that he must see the identification in better light. Have the bouncer take the wallet into his hands briefly, plant the card, return the wallet to the spectator and point out this individual to you before you begin your act.