Are you saying you want to extend the length of a cable? If so the first result on the second link you posted: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
should do the job. The first review says: " It does two important things, it extends for short corded power supplies and it makes it easier for compatibility."
So if your looking for an extension cable, it should do just that.
Yes, the 4/8 pin extension cable is made for that purpose. I've used them on some of my builds when the PSU's CPU power cable wouldn't reach the header running the cable behind the board. The cable only contains +12V and ground, no many how many wires it has. The +12V will be on one side and the grounds will be on the opposite.