Please???

I have been trying to have Max say "please" or to do the sign for please when he wants something. He can say tons of words and can do signs for words, so I thought this would be no problem. He flat out refuses to even try to say it or try to do the sign. I even tried to give him a little gum the other afternoon to try and pull it out of him. It was a complete failure.
Here is a little glimpse of what he looked like...