This can be one possibility:

http://www.youtube.com/watch?v=yF-7LcMHTn8

I never done myself, but looks OK..

1. If you are talking about diesel car then waste heat in terms of exhaust gases can be inducted into combustion chamber by using EGR method to reduce NOx emission.

2. In cold weather, waste heat can be utilized for air-conditioning system of car to warm-up the interior of car for passenger comfort.

3.This waste heat can be used to warm the induction charge specially in HCCI/PCCI engine to control the combustion.

One more use of car waste heat i got into my mind that is-

car waste heat can be used to maintain fuel in liquid state in cold weather by supplying this waste heat into fuel tank, specially in the case of diesel engine.

If you happen to have a liquid (like sodium acetate) with very high heat capacity, and relative medium phase transition temperature, then you can store the heat into that liquid, and when needed, induce heat dissipation by triggering phase change, similar to how heat packs work.

There is this interesting article that i came across and is related to your topic

https://www.asme.org/engineering-topics/articles/automotive/using-waste-engine-heat-in-automobile-engines

Suggestion of Mahmud Dwaikat sounds intriguing. How easy is to get sodium acetate? [are such liquids available? Price?]