Its possible to perform a double barrel roll within the same jump!! albeit its one of the hardest techniques to do.
If you jump and perform a barrel roll, depending on the track inclination the boost from the first barrel roll on landing will keep you airborne for a little longer. Since you used the boost from the first roll you can roll again to get a second boost!
I've only managed to do this once on Ubermall, the straight before the finish line since the track goes up and levels out it is possible to use this technique there