My team has never done a demo with more than 1/4 of the field (becuase that's how much carpet we have). You just need to put the goal in the corner and load tetras from an opposing corner.
Another Experience:
Before last years robot was taken apart to build our little bot we were given an elevated carpet square thing measuring 16 feet by 16 feet. We had barriers around so no one got to close, and the mobile goal. We were a ball picker upper so we'd bring a bunch of balls, but a couple on the square, pick them up with the robot, then release them for the kids to shoot into the mobile goal. People like interactive demos

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