Greek Shift Here we go: Control the card you want to force to the top ...
Forcing a Card First, take a look at the top card, A good time to do this...
This deck is cut in sort of a subtle 'trianglar' shape. meaning the top is wider than the bottom. therefore, if a card is place in upside down, the wider end of the card now matches with the decks lower end, thus making it easy to locate or even slip the card right out of the middle of the deck. Pretty nice deck.
-From Justin Johnson
In a stripper deck the cards taper at the ends, that is one end of each card is slightly narrower than the other. It follows that if a card is turned end for end it can be instantly found because of the projection of its broad end amongst the narrow ends of the other cards.
-Encyclopedia of Card Tricks
Basic Ways of Handling the Pack
Turning the deck imperceptibly for the return of the chosen card is very important. To begin with, have the narrow ends nearest your body so that when the chosen card is returned to the reversed deck the projecting sides will be at the inner end. To effect this reverse, spread the pack in a wide fan in the left hand from left to right. As soon as a card is withdrawn close the fan by placing your right hand on the left side of the fan and closing the pack towards the right, thus bringing the narrow end pointing to the left and the wide end to the right. Retain hold of the cards with the thumb and fingers of each hand at the ends.
If the spectator, has taken a card by its wide end and has not changed his hold, you offer the deck to him in your right hand, slightly spreading it with the thumb and fingers. Square the deck and the wide end of the chosen card is at the inner end. It may happen that the spectator will turn the card round himself in showing it to another spectator, in that case you offer the pack for its return with your left hand again slightly spreading it fan wise, this time with the left thumb and fingers. By holding the pack in the position named, the necessary turn is half made and can be imperceptibly completed by taking the cards in the right hand for the return of a card, or nullified by taking them with the left hand.
Another very good method is to square the deck and hold it by the ends in the right hand, fingers on the outer wide end, thumb on the inner narrow end, square the sides of the pack with the left thumb and fingers, the left forefinger curled up under the pack, and the right forefinger curled in on the top. Now it is an easy matter to riffle either end of the deck for the return of the card. If the spectator has not turned his card, remove your left hand from the pack and with it pull the right sleeve a little, at the same time turning the right palm upwards bringing the pack upright, right thumb on the narrow ends. Bring the left hand against the face of the deck and riffle with the thumb for the return of the selected card, simply riffle the wide ends with the tip of the right second fingers.