ETA: I prefer to use the strap keepers, because they can be used on a wide variety of bags and straps of different widths to manage the extra webbing length. But if you want an alternative hack that I used before the strap keepers were available, I used to insert the plastic tie from the top of a Peet's Coffee Bag inside the webbing loop end at the end of the Luminary shoulder strap. For most other bags that I'd make the adjustment, the webbing section would be too long and thick for this to work as well.
I'm showing you the actual length that I have to roll up on a Luminary 12 (Nebulous Grey/Dawn), and I'm likely about your height and size:

This is the section of webbing that I need to roll up. The plastic tie from the Peet's Coffee bag is inserted in the end (this is the same kind of plastic tie that
I used to substitute for the nose bridge of a mask in a different post. The tie exactly fits the webbing loop for the end of the shoulder strap.

Here's the rolled up section of excess webbing from the shoulder strap. You can bend the end of the plastic tie around it to secure it. This works in this case because the excess webbing length in the Luminary 12 is so short compared to the typical cases you have to deal with, and because the strap is also narrower than most cases. The webbing strap keepers work in a much larger range of cases to retain extra straps. I tend to order items that I know that I will find useful for lots of cases when I find them -- because it's such a pain to suddenly want them and find that they are out of stock!
I also use the strap keepers for other bag hacking. For example, someone asked about adding an external carrying point for a small, (non-Tom Bihn) shopping bag. I posted about
Adding a Connector point to the Icon Strap in the Bag Hacks forum using the strap keepers and
a triangle hook ordered from the Parts page
HTH
moriond