Use the story of the Monticello fountains, like Monticup does in the demo video, to make your spectator focus on the coin. That way, when you quirt it, you are sure he is looking in the direction of the coin.
Use this coin with the DOUBLE SIDED NICKEL. After flipping the two-headed coin several times (and it always comes up heads), you can say "Do you know why it always comes up heads? Because it's easier for Jefferson to spit that way!"