Here's my current method of connecting shoulder straps to the top bar of a carbon fiber external backpack frame....without drilling any holes.
(1) Form a harness by sewing a narrow piece of webbing next to the center line of a 2" wide piece of webbing.
(2) Fold the 2" piece of webbing in half to form a tunnel for the top bar to slide into.
(3) Sew the shoulder straps to the harness.
(4) Put the top bar inside the harness and tie it tightly with something like a trucker's hitch.
(5) Add 3 or 4 zip ties to keep the harness in place.
(6) Trim zip tie ends to save weight.
WARNING-Short white shoulder straps in photos are too short for most people to use.