As a racer you need to build up heat by doing activities, taking out cops, avoiding spike traps, road blocks, hitting cops with tech etc.
I did a race and some other activities until I was around heat 7. I then found an area with a hideout and repair shop close together and drove up and down the road whilst being chased and hit the cops with shockwave when I could and also used a jammer. Went through the repair shop each pass and kept this up until I hit heat 10.
You will get the trophy immediately, but having the hideout close allows you to bank the points too