Adding Shadow from a Live Actor and putting it into a complete CG environmen question

Adding Shadow from a Live Actor and putting it into a complete CG environment question mainly what are the ways this can be done? How have others done this and does anyone have a link to some good tutorials on this? Please respond if you do thanks.

Oldie but a goodie (from TV days) in the compositor, take the key shape from the live action and lay it down at the contact point, fill it with black and make it a multiply over effect. For bonus points blur the shadow as it recedes from the contact point. It won’t stand much scrutiny but it’s ok. Also the shape at the feet won’t be right but you can fudge that bit.

Or in 3D apply your character (with key channel) to a card in the scene and let it cast a shadow there. The only drawback may be the fact that the card is 2D and could give odd shadows when the light strikes at an acute angle.

I would think that you would have to rig a special shadow only light that won’t affect much else on the layer? Perhaps a special shadow pass for that object?

3pointEdit Thanks

Update: here is a quick test I did https://www.facebook.com/photo.php?v=2858638436727

Key for shadow, key for subject, subtract subject from shadow, multiply result onto 3D.