Well, as I do not use Maxwell, I cannot really tell what's going on. The above example is mainly for native SketchUp as SU does not render image transparency when it comes to shadows.
Maybe Maxwell cannot render alpha transparency either and would need clipmaps when rendering.

But in any case, if renderers can use image transparency for clipping, the above solution only works if they can either render double sided materials (or what) like in V-ray or they can ad shadow to a completely transparent material (like Thea).