Hmm… Way back in the olden days before the newfangled warp plugin we did it another way! I’d definitly recommend using the sequence plugin, but just for fun here’s another way:
1)You render your scene without the heat waves in a low resolution
2)Parent a low-poly sphere to your heat wave particle mesh
3)Assign the low-resolution movie to the particles
4)In the material buttons for the spheres, set mapping to “Win”
5)Re-render in your normal resolution.
This technique is awesome for making “nvisible” creatures that blur the background as they move
Some drawbacks of this method are you have to render your scene twice if you make any changes and it can be time consuming if you have a complex scene.