Yes, I have done this. Although, we carry our own decorations. I always go to see the Matre'd and order a cake. It doesn't cost much.
My cruise group does this every cruise. Regardless of whether it is actually someone's birthday or not. We create un-birthday's if no one is having a real birthday. The last cruise everyone was in on it. We gave my db a surprise birthday. It was fun. By the way, it wasn't his birthday.