There is a new easiest level to do this on! If you have the ODST campaign, load up Uplift Reserve, make sure ALL skulls are turned on, including non-scoring, and that it's on Legendary, and just blaze your way through.
You may want to practice run in through on a lower difficulty first just to get the hang of it, but the level only takes about 3 minutes. Check this video for a good path to take. It took me only maybe 10 tries to get it perfect on easy, but when I went to record this video, it was my first take.
3 spots to point out: You MUST hold
while going over the rail, as viewed in the video, while going up onto the rock immediately after (honestly its miraculous I didn't die there), and one last time at the final little ledge right before the end of the mission.