Alpha channel shadows? Re revit

I'm using revit and impression together by exporting to auotcad.

It's not an ideal process.

I'd like to get the shadows into impression. I've created an elevation view and overridden everything to white so I see only the shadows. In photoshop I'd be able to use this as an alpha channel. I read that impression supports png, so I think I can get just the black shadows. What I need to do is turn those into a fill area.

Does impression take shadows from 3d autocad?

Bump.

Hope a Guru has a light Friday and spends it at AUGI.