I tried the other solutions without success. I went to the airport like they suggested but after missing a few times I fell down into one of the tunnels and found this:
Not all of them work though, you have to go to the position below because the rest have a ridge that acts as a wall. The southern entrance to the western tunnel acts as a ramp which is perfect for low speed barrel rolls.
Get up to about 65-70 mph and put the wall right in the middle of the car. Then at the last minute turn just a tiny bit towards the tunnel and you will get it. I tried it several times and got it at least half of the time.
Here's a video I made for further explanation.