Solution to softening canvas.
After posting my question I did some searching on the internet and discovered a possible solution.
I took the bag and soaked it in a bucket of water with fabric softener. Then, I ran it in the dryer (without heat) for a couple of hours with 6 tennis balls and a couple pairs of Vans shoes in order to give it a good beating. I think it helped to loosen-up the canvas a bit, and further general use and exposure to the elements should take care of the rest.
I should also say, this particular F-3x has been to Central American a couple of times, and through the wash about a dozen times -- all in addition to the recent tennis ball beating I gave it. The thing is starting to get a nice "I'm not a camera bag" look to it, but it doesn't show the slightest hint of seam wear or other indication of coming apart. This quite a statement of craftsmanship and durability!
Similarly, my F6 got dragged through Haiti on two recent assignments (sometimes literally), and after wiping the dirt off, one would never know it ever left my house.
On a side note - I think Leica users would love to see a F-3x specific insert that would hold two bodies on end with lenses attached, as well as a couple extra lenses. A rectangular insert with two small square pockets on one end, and a diagonal divider separating the remaining space for the two bodies would work really well. The little velcroed divider piece that comes with the bag is a little too wimpy to keep things really organized. Just my take as a heavy Domke bag user.