Casting shadows from matted video footage into fog

Ok, this is probably a tough one (at least it seems that way to me..)

I have a shot of cellar doors - the doors open - camera exposure stays the same so the sky and light spilling into the cellar is over exposed. I made some fractal noise fog (with the turbulent displace effect) and an actor walks through the shot, climbs up the cellar stairs and exits the cellar. I've also applied the CC Light Burst effect to show some light rays and to better show the evolving fog.. Trying to get the effect moving enough but subtle enough to be convincing is really a challange! Gotta love this stuff!

At the shoot we couldn't get the fog machine working and ran out of time so we couldn't go get a pot or something to heat the fog juice up on - (spent too much time trying to fix the machine, should've hedged my bet and sent someone immediately) - hence the AE fake fog.. Looks ok but I'm still working on it's realism.

What I'd like to do is to have the actor's shadow cast across the fog - as it would in real life... I've animated a mask around my actor and set it to subtract - it's a start - it effectively removes the CC Light Burst which is good, but in real life the actor would cast a shadow which would be visible in the fog. I thought that I could then copy that mask, apply it to a solid, maybe expand it or something to get the "shadows" to look the way I want, but no luck yet - well, not much anyway..

Any suggestions (I know, reshoot - that's not an option at this point though..)

--KTFA