I have a metal knee which always sets off the detector and have been subject to secondary screening hundreds of times. I carry no documentation and simply tell the gate screener that I have the metal knee before I can be threatened with secondary screening for not removing my shoes (which I never do) and I then promptly walk over to the screening line. I make it clear to them that I have been thru this many times and that their best course is to get done with me quickly. Why they refused to let the LOL with the hip thru puzzles me. You know that there must be something more to that story because it just cannot happen that way and that all the letters, x-rays, scan results and even the doctor in person with his hand over his heart swearing he put the metal part into you will make not a whit of difference to the TSA.
When I'm shown where they want me to sit, I simply loosen my belt and put up my right foot (their manual says right foot first) and frequently this pre-empts a request to remove the shoes. I would guess that nowadays the shoe carnival happens to me about half of the time.
I can't imagine that carrying an x-ray or photocopy would be of any use because they are still going to give you the same shakedown that you would have gotten without it. The best way to short circuit the inspection procdure is to use the same location every time so that some of them get to know you. And then it's a breeze.