You would like to extract the shadows - not a light works trick. Easily done in Photoshop - all ArchiCAD illustrators need Photoshop.
Soft shadows are made, in part, by greatly increasing the divergence of numerous overlapping light sources contained in the Sun Object (LightWorks in ArchiCAD - pages 30 and 41). Sort of like in The Adventures of Buckaroo Banzai Across the 8th Dimension (1984) where Dr. Lizardo, attempting to cross into the 8th Dimension improperly focuses the rays of his oscillation overthruster, crashes, and ends up in a mental hospital.
Don't let this happen to you.
Dwight Atkinson