I came up with this trick while playing around with Eriksson's Shuffle.
Hold two balls in one hand. Start by making a vertical throw, while that ball is in the air shift the grip of the other ball so that you are holding it with your thumb & little fingers only. Point your remaining fingers straight up. Let the thrown ball peak & fall. As it comes down use your fingers to push it horizontally into your empty hand like a Slam throw.
Practise this move with both hands.
Now take all three balls & hold two in one hand & one in the other. Make a short vertical throw as before, shift the grip of the one still held in the hand to get ready for the push. At the same time as you push the falling ball, empty your other hand by making another vertical throw. Push the falling ball into the base of your now empty hand & grab hold of it using your thumb little finger so that you are ready to push the second vertical throw. Each time a ball falls make a vertical throw to empty the hand on the other side & push the falling ball into it. Simple.
This trick looks good when used to switch directions of a two ball 'push Shower' (which I'm sure you can work out).