How can I advise our homestay student to eat western style ?

Really? Yeah, I think his action lacks respect for you. Why not try talking to him? Then he has to talk to you and probably won't put his face in the plate.
Besides, you might tell him directly that his action is not correct and persuade him in behaving well.

Thank you Seth. He is a very nice boy but it is hard with some things for both of us. I found Google translate and explained gently a few things, I think he was okay with that and that evening at dinner table explained some of their customs in their home.Thank you again for your help.

Having just returned from China, I think you just need to explain to him that YOUR customs are different from his. For instance, in China, the tables are often times taller (made with longer legs) than western ones so the distance from "bowl" to "mouth" is not as far to negotiate with chopsticks. Also, have you explained that Westerners do not lean close to food, rather sit with back more upright, so food must travel further distance. When you explain this, he may wonder why in the world you would do that, because you may drop food and waste it. Hope this helps.