I tried using exclusion as you said, but the closest I can get is to have my light casting shadows on the ground only, BUT the light still lights up the ground. When I exclude illumination, it seems to exclude shadow casting as well.
An example of what I'm trying to do is: I want a room lit with multiple lights, with people walking around in the room. And I'd like those people's shadows to be directly below them, even though that's not accurate to the room's lighting.