This is a shuffle which is commonly used in card tricks. The basic idea is to have a certain amount of cards for example the 4 Aces and you want to give the illusion that the whole deck is being shuffled when the aces stay on top the whole time. Take the deck and have the cards on top that you do not want mixed. Shuffle them in a regular shuffle by splitting the decks in two and then riffling them together. But when you come to the point where the 4 aces are you let all the cards in the opposite side fall before them and then let the stack that the 4 aces are in fall. If this is done fast it will look like a normal riffle shuffle.