Faking shadows on semi-transparent particles

I'm using Edelwiess' Cloud system which renders particle cloud masses. The clouds currently do not support shadows or projectors because they are semi-transparent, so I was wondering if anyone knows a way i can make fake shadows that are casted by the clouds and/or receive shadows from other objects (specifically the player)?


His system is using both custom shaders and Shuriken to generate cloud masses on polygons I believe.

Here is a snapshot of clouds in my game:

 

I'd say a top-down render of the cloud map then use a projector to project that top down texture onto the level is the only way to have proper cloud shadows.

 

Ah, so basically, just project a render of the cloud using a projector to create a shadow. Smart Idea. Though, I'm hoping that I can find a way to project a shadow someway onto the clouds...