Being as how the snow cat showed up before I had a chance to use my spare as an anchor, I can only tell you how it was supposed to work

The idea is to minimize the vertical force on the tire so you are only pulling it laterally through the snow. Snow is actually quite strong this way. Consider the idea of stopping yourself from sliding down the side of a mountain with an ice ax.

To do this I buried the tire as far away from the Jeep as possible, in my case about 100' away due to the length of my winch line. Doing this minimizes the angle of pull, resulting in very little vertical force being exerted on the tire. In addition I planned to dig a small trench for my winch line to get an even more direct pull. After I dug the hole I compacted the snow along the outside of the hole to help distribute the load more evenly on the surrounding snow. Now I had the 100' of snow between my Jeep and the tire, holding the tire in place while I winched out. I then would have thrown a large pile of compacted snow on top of the tire to help stabilize it.

Ideally a log would have worked much better than a tire because of the log's greater mass and larger surface area. However, I did not want to cut down a perfectly good tree, so I decided to try my tire first. After all, I'm the one who got stuck, no reason to punish a tree for it

Sorry for my ignorance, but what's a "come-along"?

It's like a strap winch you crank by hand. You often see them used on trucks to secure cargo.

Here is a big version: