I did have a double block, 2:1 set up as you describe on my old Nacra 5.5 with spinnaker. The problem was the line kept twisting around itself and caused problems on the set and the takedown, but I was pulling it all the way from the tramp, no mid pole snuffer back then.

With the mid pole snuffer, the tack line only has to go out about 4 feet, so I figured a simple single line to a single block would be enough.