That's horrible Perhaps you can try the police dept. and see if they can do anything? It seems around here police are very helpful for these kinds of situations.

If the dog is still there, I would take a water bottle, and aim the water through the little opening to at least get the dog a little wet. The owner might get mad at the wet dog and car.. but if it'll keep the dog cooler, then I really wouldn't care if I pissed off the owner.