You probably worked this out already, but...

Unticking the Visible flag means that the figure/object/actor is completely ignored in any renders; i.e. it can only be "Visible to raytracing" if it is "Visible".

I understand that the correct rendering of transparency requires raytracing, so what would happen if you made the figure completely transparent and used depth-map shadows? I don't use depth map shadows myself, so I don't know if they respond 'properly' to transparent objects. Just a thought....

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)