Link to directions to attach an umbrella to a backpack:
Not sure if this is the one you refer to, but it's something. I have no experience with this.
I did try a different approach once, haven't used it enough to make up my mind about it. I got a couple of small velcro bands, used those to attach the handle of my umbrella to a trekking pole (downside: I *still* end up with only one trekking pole, maybe a nice local stick would work instead ...).
Note that I don't use baskets on my poles.
Attach the pole so the point is up, handle down. Run the waistbelt of the backpack through the wrist strap on the pole. Tuck the pole/umbrella handle under the chest strap on your backpack. Try this at home, walk around a bit, decide if it would just drive you crazy or not ...
One issue, I think, with any hands-free solution is adjusting the angle of the umbrella relative to where the sun is coming from. Less of an issue when you're trying to block out rain, though here too it's a factor, especially with some of the smaller diameter U.L. umbrellas, like the montbell.
Keeping the direction and angle close to optimal is particularly challenging given that any hiking trail twists and turns, you're rarely walking in a straight line. Holding the umbrella in your hand, you adjust almost unconsciously.
For rain, I've gone to a poncho and don't carry an umbrella.