This devise addresses access to the hook end of the fly. Just remove the Danvise jaw, insert the extension, insert the jaw into the extension and tie away.

http://www.jsflyfishing.com/

the site below has a discussion and pictures.

http://www.westfly.com/forum/ultimatebb ... 325#000000

they are also on Ebay from time to time. I was surprised that Al Beatty did not have them, but they were nowhere on his site.