Purely speculation - you can probably rig something up. I don't know if it is possible to purchase that bottom portion of the cord, or more importantly the lower half of the connector to attach a cord to so that you are able to easily disconnect/reconnect the shoulders and the back assembly.
Assuming you can, this is one of the rare minor modifications I might feel comfortable doing for a customer that isn't actually altering the essential operation of an item. Approach might differ depending on how much you want to sheath the line to avoid any possible snags caused by an unprotected cord running several inches across your shoulder.
My first thought is to get some split rings smaller than the diameter of the pull knob, and attach them to those fabric daisy chain loops on the shoulder. That would give you multiple rings to run the cord through.
My second thought is that I could run a line through and behind the mesh fabric on the shoulder strap, without sewing anything into place. Not sure how smoothly that would operate once the line is curved over your shoulder, or if it would eventually wear on the shoulder mesh and enlarge the opening. But there wouldn't be anything out in the open to snag.
PM me if you want me to research that part, and give you a quote on part + bladder + anything else related.
