I came up with a pretty cool way to attach my Montbell UL umbrella to my pack this summer for hands-free use. I use two Camelbak Tube Traps attached in opposite directions to the webbing on one of my shoulder pads. To my surprise, Montbell's shaft clipped right into these Traps, almost like it was meant to be there. At first glance the system seems unstable, but it held up remarkably well to heavy rain and wind, and to lots of brush overhanging the trail during my Long Trail thru hike.
By switching the direction that each Tube Trap was facing, I could cause the umbrella to "lean" toward my left or right, which allowed me to protect my pack very well. I was also able to adjust the umbrella up or down to provide less or more protection depending on the ferocity of the storm. All in all, I was much less wet than my hiking partners, and I always had both hands free to use my poles. I also got lots of compliments from folks who saw the umbrella in action... I suspect it's a great way to meet members of the opposite sex!