Moss on shadowed side of stones?

[Evilsoap]

Im a newbie and Im still in the process of discovering TG2 Thanks to many of the excellent tutorials and tips in this forum I have been able to setup a few scenes of my own and that´s when trubble starts.
In nature most stones, trees etc that faces away from the sun have more moss and liches than the sun side and snow thats in shades areas (behind stones etc) tend to be thicker than snow lying about in the open. Is there an easy way to replicate this?
I have seareched the forum for clues but not found anything i could use (or understand:).
Could I do this with functions?

[Dune]

I don't think you could. But thinking this over, you could try to convert the shadows into a mask. Render a picture (perhaps with exagerated shadows), make a negative (in PS) to make light areas where the shadows are, and use this as a sort of through camera mask for snow and moss. That's the only crude method I can think of. Or use the painted shader.