As you know most shaders use the dotproduct of the normal and the view vector to generate this cell shaded effect you have now. What you can do is instead of using the dotproduct to pick a color, you can use it to sample a mask and then sample the color using the mask. This is how you do masking with shaders in UDK:…
@whiketan Thanks so much! Could you explain further what you mean by making the face more planar, do you mean much more flat? I added a couple tris to give her a nose, but do you mean to remove that?