Anywhoo,
Pucker your mouth as if you were to whistle. Now, instead of blowing air out, use your tongue to push the air out through the hole to create a short noise (roughly a half-second long). Do this a couple of times, and after familiarising yourself with the noise, flick your cheek with your finger as you push the air out in order to create the sound.
It really sounds quite exquisite, and you can achieve several different noises by flicking different parts of your cheek (i.e bottom of the jaw)
Just thought you guys would want to learn...