These could sell decent in the store I would think. I actually have one similar to this already

I made it from parts I had here, for the same reason, not to have to open the case to pull the power ect. I put a female plug in the hole in the back of my CarPC case, and hot glued it from the inside. I did it this way as to not have a pig tail or wires dangling out the back of the CarPC when I move it around. I can just plug the male plug into the back of the case, and it locks in place.