You don't have to do anything. You're doing it because you want to.

I have friends who are shopaholics and spend too much. Sometimes they get a bill and want me to pay for it and I don't do it. I tell them to sell that new dress or shoes they bought and pay the bill. It's not like they need 20 dresses right now, but they have to pay the bill now.

Looks like you need to teach your friend about priorities before you teach him about saving money.