you've got a couple ways to do this.
You can use your thumb and wrist which is how most of the greats do it. It just takes a lot longer to get down.
or you can flip your hand over and use your pointer and middle fingers alternating to push the stick down.
I generally use moller though.
And lastly you can use one handed rolls.
RIGHT HAND:
stick is at 90. arm at zero.
throw the bead of the stick down for the first hit.
your hand should be at a downward angle and u should let the stick come back up to 90.
the key is to not choke the stick and stay relaxed.
the second stroke happens during a combination of your fingers and your wrist coming back to the starting point.
HUGE TIP:
Utilize your thumb to get a little more power and control in the strokes.
LEFT HAND:
I was refering to the buddy rich style roll. Which i can't do YET so heres a vid with explanation.
http://www.youtube.com/watch?v=A-4s2yN6PIE