I've got this character mapped to a plane via an alpha channel.  I want the character's shape to cast the shadow, instead of the plane it is mapped to.  Is there a way to do this?  I know years ago I used to do it in Bryce very easily, but I can't seem to figure out how to make it happen in Carrara.  The texture map will be animated, so mapping the image to a shape cut the same as the image will not solve my problem.  Any ideas on how to create the shadow from the mapped image?

Chucker