Very Big Striped Cat update: I tried everything suggested to get the smell of male cat urine out of my car. I finally resorted to a professional cleaning, and the car seat still stinks!
The cat is doing better than my car seat. It turns out that he loves big, dumb dogs and aspires to be a house cat. He has settled into his foster home, following three dogs through the doggy door, sometimes between their legs. He could jump the fence to freedom, but hey, there's food and a soft bed back inside.