I don't know how else to explain this other than what is already in the guide:
Head back to the bowling mini game start point and look at the large red loop in the back corner. On the ground level there is an opening so go inside and turn left up the blue ramp. Go as far as you can and fall over the edge for (CP235) Hot Rod Walls then drive through the blue tunnel to exit. Turn left and stay along the wall. Turn left again and make your way up the big blue ramp back to the top. Stay in the middle while going up for (CP236) Pilot Hat.
Here's the pic:
It's right in the open. Are you sure this is what you are missing?