Node Material blending/masking question

Greetings. I’m currently using Blender internal rendering system and I’m trying to test a working way to blend materials together for various geometry areas smoothly without using any textures.

For example I have a head and I wish to have a base skin material on bottom, then add another material for lips.

Is there a way to use vertexgroup or vertex color information in nodes to mask materials?
Or do you have any another suggestion? Thank you for any possible information.

check the tutorial on ‘stenciling’ in my signature, it is for an older version, but it is fairly basic and easily translatable