If you get the boost of speed between the BRs, you've touched the ground, even if it is only for a fraction of a second.

What I'm trying to do is to avoid any confusion: you cannot do two barrel rolls during the same jump.

Like I said, grab a turbo, head to Ubermall forward on the long straight and take off from the hill before the finish line. You will only be able to do a barrel roll once, and will not be able to perform one again until you've landed on the ground (Which means getting the burst of speed).