How about dribbling the ball from below. As you drive around you start bouncing the ball straight up in the air. You only have to add a small amound of energy with each bounce thus everything would be quite safe. With each bounce it gets higher and higher and as you pass under the overpass you stop the robot and the ball keeps going. Then you run under the ball and catch it for the next lap. I think a robot that can dribble would definitely earn your team some kind of technical award.