15 minutes only got me this far. But I did put the box back together, fill it and put it away. This time I was careful not to put any Bionicle or Lego pieces in it. He plays with those every single day. He won't want the box if he knows it doesn't have any Legos in it.
Someone suggested that I make a huge drawstring bag that can be opened up and laid flat on the floor for the Legos. When he's playing, it's a mat. But, when he's done, I pull the drawstring to close it into a bag again. Then it can be hung somewhere, out of the way. I like that idea and may do it. I'll post about it when I do.