You should act the same way. If he is sitting at the table waiting for the next course to magically appear in front of him, open up a good book and start reading, eventually he will have to communicate. You have not indicated that he is such a boor that he would be absorbed in his own world, only to join the conversation long enough to say, wheres the food. If it bothers him that when he wants to communicate others are engrossed in their own things, he might figure out all by himself that he is engaged in the same type of rude behavior.
I dont know what type of sense of humor your son in law has, or your relationship with him, but why not try the humorous approach? Why not call his phone, or send him a text asking him if he is ready for the next course, or what he might want for the next course. If he is connected to your facebook or twitter account, perhaps tweet the news that the next course is ready to be served. He might get the hint, or he might ask why you did it which gives you the opening you want to explain how his behavior is rude and boorish.