There is no easy way to do this if you want some quality results. I did something similar at the ad agency i used to work for and you'll need a 3D app to do it.
What we did was overlay a basic 3d head on top of the models head to match the measurements and position and then used the explosion FX filter to it.
Then we took the gray model to Photoshop and manually painted the tiny corresponding face part to the each flying particle. Took me a whole week to do! We used Cinema4D for this and as i said this is not as easy as the client seems to think, so get C4D if you don't have it and charge it on him!
Here is an early screenshot of the head, i don't have the finished one but is it something similar to this you want?