This will take some practice, learn the course well. I will give a few hints which helped me shave off a few seconds or gave me some boost. I'd say this took about 15-20 runs to get it. I did it 34.6
After the first ramp on the left, as soon as you land, start cutting over to the right for the ramp to the upper route. This will shave off precious milliseconds by taking the inside route.
If you take the big ramp in the middle of the race that launches you into the giant stack of boxes, aim for a corner of the stack. You get little bits of boost from the boxes and by taking a corner, then middle, then corner, this could give you enough to fill a boost meter each lap. Boost as soon as you hit the ground after that jump.
Right after that where you have to weave through explosive stacks, I didn't pick a pre-planned route, I just went whichever way didn't require any wide turns. Keep in mind there is rows of boxes here as well, which could again give you a boost.
Now the end, this is the only thing I planned. I used the high ramp on the right for lap 1 & 2. On the final lap, I took the left path, which hopefully will have a big stack of boxes which should fill a boost meter and burn that boost immediately. Jump the explosive boxes & hit the small ramp which should get you over the finish line quickly.