start with 2 chord songs. Anybody who plays ten chord songs but hasn't learned to listen for a two chord change is a pain in the arse and bound for a life of discontent and misery.

Get him to sing ALOUD to the chords. if he's too selfconscious to do that get him a harness with a kazoo. tie the harness to the back bumper of your car, and drive around the block several times. Say, now will you bloody sing!

tell him to study accountancy - ultimately its probably more fun.