Shadow catching in Physical render

[Freemorpheme]

Is it possible to render out an alpha with some shadows in using the physical renderer?

 

I have a legacy product file using soft ground shadows using mostly AO, and I need to render it out on a transparent BG with the shadows intact, but in my test file I can only get the shadow catcher to work with the Standard render.

shadow catch test.c4d

[Jeff H1]

is this what you're going after?  A shadow pass?

 

[Freemorpheme]

That looks like what I want, except when I try it in my real scence I just get the shadow catcher in my render. Is that using the physical render?

EDIT I think its because there are no physical lights in the scene and the GI doesnt respond to the shadow catcher - although some experimentation reveals physical render is not the issue. Perhaps my question would be better phrased as 'how can I catch the AO shadows in my render?'

shadow catch test.c4d

and no shadow

Edited September 4 by Freemorpheme (see edit history)