i've been doing the super flip utility for years. it is a knack, and you have to get used to it, let your fingers get used to the feel. my tips would be, don't try to flip the last card. if you do, you will end up with a clumsy, obvious appearance in the flip. instead, just concentrate on the dribbling of the cards. as you near the last few cards of the deck, touch your index, very lightly against the edge of the top, and allow that to be the counterweight against it. don't make the flow of the cards too tight, as this will impede the amount of space available between the cards, making it far more difficult to flip the card(s). instead, make the dribble light and rapid, with a distance of about a foot and a half between hands.
hop this helps.
C!