I haven't tried it yet, so not sure if it will work, but have you tried the new plant generator in C8? It would let you add several "leaves" and I think leaves can be any objects, so spheres should work too. And you can shade them differently to create some variety. If I have time, I'll experiment with it myself tonight, but that's the general idea.

You might have some trouble with realistic SSS, though (depending on your light and how close to the grapes is your POV), at least that's what I had most difficulty with last time I was experimenting with grape shaders.