You can do this, within a performance, say you are doing three effects, after the first effect you do (the opener) spread through the deck face up without letting them see the faces and search for a card, take this card out and tell them you will save it for later, hopefully this card can be sucessfully psychologically forced, if you dont want to take that road, just take it out and leave it in your shirt pocket. Tell them you will save that for later. Go onto the second effect, then thirdly end with the card you just placed into your pocket.
You can go onto a mind reading type effect, or just do Roleplay, but with the Advocate.