E+ doesn’t allow to define material properties for shading elements (louvres, context buildings, trees, etc). Only transparency. The only element you can define them is Lightshelf, which won’t be appropriate for your case.
You probably need to create a coupled model that combines results produced from Radiance and use them for the E+ simulation.
There is an example in hydra showing how to do that.
Not the good news you were expecting, but news anyway. Hope it helps.
-A.