At the end of second day of burning. Just playing around with fire.
I noticed a small rotted area about a foot from the edge of the stump, so I cleaned it out. At the bottom I found a cavity going out to the side, so I dug a hole about a foot deep outside the stump. Using a screwdriver and a spoon, I opened a passageway to feed fresh air through the cavity to a fire in the rotted area. The root burning in the video was next to the passageway I opened. The middle of the stump was all fat lighter, so it didn't take long to get a roaring blow torch.
I've burned all the dead wood I can find in the immediate neighborhood, so I haven't decided how to deal with the rest of the stump.
Spreading out the 10 yards of dirt I got to fill in the ruts in the lawn using a bucket and hand truck only took several days. It's not perfect, but at least I'll be able to push my 21" Bolens exercise machine around without scalping anything.