shadow pass problem

i'm doing a separate pass for moving people in my scene, and need their shadows visible as well. so the lighting rig gives me the shadows i want, i've applied the useBackground shader to the scene... and turned off cast shadows on the scene geometry (shadows for the scene look best when rendered as part the main radiosity render).

problem is, now the scene geometry doesn't block the shadows of the people. its hard to make out but in the attached image you can see the people shadows passing through some matted pillars. obviously enabling cast on the scene will fix this but i don't want the scene casting... so what to do...?

This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.