You can use burned CDs.
Just dont get nervous and jumpy towards the end.
Its good to qualify last, then if there are only a few people in your class that you want, you can take it easy. If there are only 2 people qualified in the 139.9 class that got over a 133, then play it cool. Qualifying with a 133.1 and a 139.9 will give you the same result.
Then in eliminations go for the perfect 139.9. But watch your opponents score. with 10 seconds left, if they are under 135, stay at 138 or so just to prevent overshooting.