Just a passing thought... If you don't want the Ground prop to catch appropriate shadows from your scene lighting and objects, what use can it be in your scenes? Why not make it invisible?

(edit) x-post - I was away looking at something else!

"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)