The term came from visiting a restaurant and overhearing a family on an adjacent table. The young boy was called James. He wanted the same dessert as his brother but his Dad suggested that they all have something different and share to ensure more variety!
This we thought was a good idea, we now do a "James's Dad" everywhere we eat! Try it!
B: "Neither can I"
A: "Wel how about I have the fudge cake and you can have the apple pie, then we can do a James's Dad..."