I got this relatively quickly by replaying the 'escape' event South Trevino Avenue which becomes available once you unlock Sunset Hills and play a few events.
You can clear this 8 out of 10 times in about 15-20 secs. When you start there are 2 cops ahead of you and one behind. Floor it straight away and take the first left, which is just before where the 2 cops ahead spawned, then left again as soon as you can and head up the 'main' road.
There is a cool down point which will appear ahead of you on the long straight(ish) road, which is behind a fence by a garage on the left hand side of the road. Keep an eye on the radar to see where the cops are as occasionally one will spawn and block off your route to the cool down.
Hope this helps and any comments welcome