I used a derivative of Tiny's method on one ferrule, but used an assemblage of washers a bolt and nut. The key item to keep in mind is to use a bolt that is the exact diameter of the ID of the ferrule or the ferrule walls will collapse and bind on the door handle. I screwed up a new $10 ferrule in this "product development" stage. I think cutting ever so slight shallow incisions every 60 degrees or so on the inside portion of the ferrule also helps to get the correct compression started.
It seemed more art than science to the process.
