The fastest way to achieve this is with an alternate racer on a long track.
I raced with Boles Roor on the first track of the Galactic Podracing Circuit, once you hit the second flying section with no rocks, hit max speed and then perform a boost.
Look for the speed indicator on your right lower side, one the circle turns Green push
toward and a new indicator will appear, once the yellow light appears, Press
and you'll be boosting.