I hate it that such a beautiful horse has such a huge problem. I really don't know if you should ride him or not. If you did, I would advise only short rides at no more than a walk. I don't advise trying to take the heel down yet, just trim at the same angle to get rid of length until you can get some x-rays. From his appearance, he is too old for the club to be cured. I think the most you can do would be alleviate some of the uncomfortable feelings from it. Of course, I think it worth your time to try to help this horse. If all else fails, he would make a great pasture mate or even a pet for someone who cannot ride. If it comes down to having to get rid of him, you might suggest therapeutic riding centers to his owner. I think they have horses that are only used for groundwork and are not ridden, but I'm not sure.
Ok, I just read your new post. I think that the most you can do is help him be more comfortable since x-rays are not an option.