Use the Aerials map and jump as high as you can. From the start, cycle back to have a good startup. After that, jump into the ramp with a backflip to gain speed. Highs of at least "6" (over 6,000 points) are possible. Keep doing backflips for extra points (about 600 points each).
Wait for the ball to become still so you can focus on getting over a hill. Do not get too excited about the ball going over a hill. If you think the ball is going to roll back down, let it roll then try again. Since there is no time limit, take as long as needed to get over a hill.