Is it possible to create a 3d shadow model?

I was wondering if it is possible to create a real 3-dimensional shadow model.

Let me explain what I mean:

I was trying to create a 3-dimensional shadow model by making a semi-transparent black box. Everything that is inside that box will be seen darker than outside the box - exactly what a shadow does. However, there is this one problem: objects, that are behind the shadow will also be darkened by the box. The box acts basicly like sunglasses, not like a real shadow.
Is it possible, to create a model that is 100%, but darkens all objects that intersect it directly, but not those behind it?

note: It has to be done so that warcraft III can use this model.

no, it's not possible but a pyramid would allow for more viewing of things behind. it would of course also decrease cover-able things though.

just tint the model with script

It's not possible because WC3 doesn't use raytracing for the lighting.

What about the ingame unit and building shadows? Anyone know if they interact with the lighting and models underneath or just make a big splat on the terrain?

They just create a big splat on the terrain. That's actually why I am asking this question, as unit and doodad shadows are not affected by omnilights and stuff. It looks weird when a light source enters a shadow, but the shadow does not vanish.