Then how on earth does he nail a double br????

Surely you either -
A) Hug the left wall as much as you can, or
B) Drift slightly out to the right to give you more room to attempt a double br.

I did notice while experimenting last night with different lines that you can hit a double br in a similar way to the one on AP - landing on the speed pad at the correct angle.
However it succeeded once in about 15/20 attempts so bugger that idea.

I did try to shift left VERY early, so im landing a br mid corner, however no matter how much i pitched down i couldnt avoid the roof of the tunnel.