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.
I’m the supplier of the extension arm for the Danvise but do not advertise it on my site. I don’t want to compete against my own customers. If you want to know what it looks like the address below will help:
Right after I picked up my first Danvise, I was on a business trip to CA, and stopped in a fly shop in Stockton and the owner had a Danvise set up on a tying table and showed me a trick to give me a bit more room when tying. You take the jaws out of the angled arm, remove the arm and insert the jaws in the tube.
There’s space on the opposite side of the housing that holds the jaws with a semi-circle at the bottom where the lever fits in. The jaws are held in by the screw, you can see the knob above the tightening lever. I found that by sliding a rubber gasket over the housing helps maintain tension when the lever is opening or tightening the jaws. You can barely see it on the housing between the lever and the tightening knob.