Burnout CRASH!

I tried this numerous times waiting for a large group of cars, and then blowing them up myself, but was never successful, what actually worked for me, is to cause a really solid road block, with every additional car that hits the pile up, the cars in the pile will lose a bit of health.

If you can avoid using your crash breaker long enough, eventually one of the cars in the pile will go on fire, and explode, setting all of the others on fire.