I'm with Momma11 on this - don't let him write with a hook. I am a lefty, and I write normally - my lefty friends who DO hook all say they wish they had learned to write my way, too.
You can sit across from him, for him to watch you. Or, just trust that he'll get it. Heather E. had it right (ha!), too, when she mentioned not sitting so that you bump elbows. Pay attention to that at the dinner table, too.
And I agree with Mommy B. - since kids should write before they start kinder anyway, "homeschooling" is irrelevant. Besides, I want my kids to learn more than public school teaches, anyway. I think I saw it from one of the mommas here (I'm sorry I don't remember who - a lot of you ladies have fantastic things to say!), but I like to think that I DO homeschool - but I also send my daughter to a daily, 6-hour, state sponsored supplementary tutoring and socialization program (ie, elementary school).