A friend needs a way out from masturbating. what advice should i give him?

Break the habit: Like quitting any habit, your friend should avoid entiely behavioral, emotional, or environmental triggers that lead to the behavior he is trying to avoid. He should get another habit to work out the nervous energy, preferably something healthy and constructive.

Ask why: For most people, this is a way in which we learn about our bodies as teens to prepare us for adult life, and something that happens from time to time even in a stable relationship. Life's hard enough without bad advice from people who want to problematize it. Only if there is an obsession / compulsion that's clearly interfering with life is there any reason to see "a way out.".