I think that kind of thing is just easier in postwork, either in photoshop or with something like Postworkshop or Photosketch. I think it's noble to try to achieve it all within the renderer, but kinda masochistic at the same time - I'd say the image you want is the important thing, use any means to achieve it, why limit yourself?

I did this one, Huntress,  in Postworkshop, it has a node-based interface a lot like the material room. The render was from modo, not poser, but the process would be the same.

I also have a watercolour version of the same image, I'll post it here if you're interested.

Postworkshop is pretty powerful but I really like the hand-paint function in Photosketch. You can run a filter over the whole image to get almost there, then change the settings on the filter and re-paint over specific areas until you get exactly what you want, so it's quick but also very flexible.