By force i really mean try to help him to do the right thing. I actually showed him one of those videos about how to do the chairlift. As soon as one of them said the word 'butt' it was all over, plus he wanted to play Minecraft. He's kind of at that age where snowboarding to him is like playing in the snow, not really a sport with rules ,etc. So videos don't really hold his attention. Though he is always super attentive during lessons if for no other reason than it's what you do in 'school'.
I have a few others that show progress.