In this case I want the slab to pour on top of the footing. With the cut profile tool I can change the outline of the slab without using linework or filled regions.
When opening the command you may pick to edit a face or boundary between items on the green "whatever it's called bar" below the ribbon. Just draw the changes to the slab boundary. Make sure the blue arrow in the middle of the line is pointing to the side you want to keep.
FINISH and we've got...
BOOM....Free Money
Here's a video of it. Use it to learn a little more or fall asleep. It's effective at both.