Start an Exhibition match:
Difficulty: No bots
--Match Length: Unlimited
--Max Score: Unlimited
Just keep bouncing the ball off of the walls or give short bumps from your car until you break open a hole to score. Only tiles on the opposing teams side will take damage so keep it over there. By the time you have all 18 goals you should be done, or very close to finishing Buckminster X10.
Just a small tip, the longer the ball is in the air without touching the ground the wider the damage radius will be when it lands. If you can keep it up long enough it can damage up to 18 blocks around where the ball hits. Not necessary to try though.