Ignore it! He is using it as a form of control and if you acknowledge the behaviour, you are giving him the control. You either have to put him in a "crying" spot away from where it is fun and he can't see what's going on or just completely ignore him going on with your day not giving him an ounce of attention for the behaviour. It will eventually stop as he realizes that what works at home, doesn't work with you. Trust me...it works. It may take a bit but he will get it. He is totally old enough to understand and he KNOWS what he is doing.