Soft jaws are not cheap so this is a hack can save a lot of money in replacing old machined out jaws. This set up also allows for the jaws to be kept if a repeat job comes up again and again. Also you can custom make the jaw lenghth to suit the work piece (within reason). I have also setup the chuck on the mill and bored a set with a known offset to produce several cams which I wanted to all be the same.
This may be useful if you use soft jaws alot. Link to website and photos.