Search "green screen suits." Kinda of inhibiting for some models, you need troopers on this shoot.
Use a tripod.
Shoot the green model + clothes.
Model steps out of scene.
Shoot a clean-plate background.
Photoshop, photoshop, photoshop. CS5 masking is wonderful.
Or forget the green suit, but still shoot the clean-plate. Hire a roomful of artistic high school dropouts to paint out the models.