I would animate the model and then render the animation to an AVI
file with totaly pure Blue backrounds. Then you load your real life footage into "Adobe Aftereffects". Then load the animation AVI on top
of the real life avi. (still in Aftereffects)
Then you simply Key out the blue parts of the animation AVI.
Just like one would do using a blue screen.
I hope that helps.
(in a bit of a hurry, Maby explain it better some other time)
EDIT : (Can also be made using "Adobe Premiere")
This link gives some nice information on how to use a "blue screen".
Wich is what you want to do but using the blue backround rendered in
the animation AVI instead of a real life "blue screen".
http://www.spoono.com/3ds/tutorials/tutorial.php?id=9