I would start with the biddle trick, having them sign the face of the card. It is no longer one out of 52 cards, it is now unique. The card chosen mixed with where they signed the name, no other exists like it in the world.
Go on to perform the biddle trick. When they hold the deck, and the card vanishes from your hands, you can tell them the card is just trying to find its owner. Continue into an ACR with the signed card. Explaining the card still want to stand out, to continue being unique and not wanting to be lost in the deck.
You can then go into a 2CM using two kings, assuming their card was not a king. Try and end with the signed card and its twin being the ones left in their hand. As they look at their card, get ready to perform panic (I do not own it, so I'm making an assumption you are able to do this). Explain that the way 2CM worked is you actually had the kings the whole time, and everything else was just an illusion, and perform panic. They are left with a signed card as a souvenir of what you did, and you are only left with the four kings, a nice way to say you are done with your performance, and no one can ask you to do it again (Well they could, but you have no deck
)
Just an idea.
Or, take mattjones advice and just perform as long as the audience seems interested. You don't want them feeling like they have to stay and watch you.
-ThrallMind