At the starting line, turn wheel completely to the right (I assume here that you are playing against ghost cars). Hit the wall at your right and race backwards to the half pipe. Head for the white lines at the exact middle of it and press ABORT (1) as soon as your front tires are on it.

Hit 1st gear, haul ass to the top of the little hill, keep far left lane (don't tread on sidewalks), and a few meters before the top hit 2nd gear and control gas feeding. Before taking off in the air, make sure you give the wheel a little hit to be sure your car is heading right, pointing to the entrance of the cathedral alley, just after it. Land and then full gas + 3rd gear, this alley turn can be taken in 3rd with gas to the floor. You have to hit the left wall at the beginning of the alley, it will give you speed boost.

Head then to the back door behind the tree and then press ABORT (2) as soon as your car touches the sidewalk just before it. Reappear in 2nd gear, make a hard left turn and go crash (3) into the wall at your left (crash into the 3rd light spot on the wall, start counting from far corner). Definitely DON'T crash into the wall in front of you, this is slower. Better use the wall at your left. So crash there and let yourself burn.

Reappear in 1st gear, but hit 2nd IMMEDIATELY. Stay in far right lane, ready for the mech-warrior turn. Approach in 4th gear at full speed, take the little jump before the turn, then as you land hit 3rd gear with gas feeding controlled and point to the interior of the turn. I mean you have to take it as close to the apex as possible. The closest to the interior you make it, the fastest you will get out of the turn. Remember: 3rd gear with half-acceleration i.e. push gas pedal in a half-way. Then as you are in the turn, full gas and hit the wall at your right at the end of the turn. It gives you speed boost.

1st lap: the train area. Approach in 4th gear full speed. There is a yellow/black wall before the train, hit it in the exact middle with the front of your car, then bump again on the train, it gives you little speed boost. No speed loss there.

Haul ass to the part before the halfpipe (houses..). Approach from far right, cut into the grass, then cut to the fence and bump on it, hit then 3rd gear and cut the house still in 3 rd. Bump into the house at the exit of this turn then haul ass to halfpipe STILL IN 3RD GEAR very important. Make the halfpipe by using the lower middle of it, don't go too high on the halfpipe, you would lose time there.

Then as you approach the finish line / checkpoint, find the best spot where to hit ABORT (4) to go back to the halfpire and do the crash/abort cheats again & again.

My time using this method is 3'48"31 (against computer clones, it's faster )
laptime: 1'11"04 (using crash-into-the-trolley technic)