Came across IvyGen – http://graphics.uni-konstanz.de/~luft/ivy_generator/ today and have had a bit of a fiddle with it.
I swapped out the default lambert shader that it comes with and put in a place a mia_material_x_passes shader, along with a bump map made from the leaf textures, a reverse/luminance set of nodes to pipe into the cutOut.Opacity of the mia_material.
Had a fiddle with the settings and am quite happy thus far, although as usual there is always room for improvement.
Only problem I am having now is with Linear WorkFlow. I think it was invented to give headaches, but I think subject deserves it’s own entire post.