It's actually really easy to get a big highscore. I started bouncing at 300.000ft and stopped at 1mil because i was really bored after almost half an hour. Note that I only had around 120 upgrades, and no 200%'s on the launcher boosts.
So I put an armadillo in a cannon, launch it with a speed of 300mph, make it hit and pop over 20 baloons on the way down, make it hit the ground at 200mph, then make it bounce up again to do the same thing over and over again, to make it later hit around a billion mines and let it land after 1 million feet? I don't think this is completely legal...