How about drastic measures, like selling his car and replacing it with a bike, explaining to him that they can't afford the running costs of the car anymore etc.
I just feel like he needs to be shocked into understanding the situation. Because she manages to make it work, he thinks they are fine. He needs to go hungry.
I know, so much easier said than done. It sounds so horrible. I really feel for your friend, I hope he snaps out of his self absorbed money wasting attitude.