You probably have noticed that Z-buffered Kleig light soft shadows (most of what we use) are not rendering soft.
Shadow cast on Ground Plane...
However, it turns out that models can shadow themselves correctly. So...
Use the Grid wizard to add a flat plane to your model and give it a bone that is independent from everything else in your model.
In the Chor, constrain that bone to the Ground, then set the Ground to OFF.
You can scale that bone to scale the plane to be as large as you need.
Shadow cast on plane that is part of model...
Of course this won't work when you have more than one model in a chor. For that, take your project to V18 and render there.