To reiterate my words from the "Part car, part plane" solution:
If you follow EX slay3r's awesome solution for the "Nadeo Space Program" achievement, then you'll be able to easily whack out both this and the "Part car, part plane" achievement pretty quickly (so all credit goes to him!).
Load up that particular track, hold down
, and once you've gone past 500 metres as you fly upwards, immediately press
to go back to the start and simply repeat the process, spamming
to restart when you run out of credits. Your speed gauge will always reach 1000 before zooming off the edge so you'll be getting another count towards the 100 for both of these achievements in seconds.