Is it possible to render the shadow of an object but NOT the surface the shadow is being cast on?

The scene I have, has a character standing on a grid plane.

I'm trying to just render my character and his shadow so that it will look like he is standing and casting a shadow on the ground of the new footage I'm going to be comping on top of.

Thanks

Check out the VEX ShadowMatte shader. Placing this on the grid in your scene and rendering the character as a phantom object you will get the shadow of the character on the grid in the alpha channel of the final image.

I have attached a demo file with take takes in it.

MAIN=>render both the character (sphere) and the grid normally.
SHADOW=>the setup as described above. Check the alpha and you should see the shadow only.

Hope this helps.

NICE. Thanks for your help. Just what I was looking for.