It worked best, after examining the photos, to fish a fish tape through there. There is no way to get the wire to go into the right place by itself. Of course, it would be easier to cut the wire at the old antenna, and tape the new antenna connector to the old wire, then pull the wire through. But, instead...

After removing the stock antenna, I went underneath the dash. I removed a small piece of foam that blocked a opening about the size of my fist (the foam was just resting jammed in there without being attached). I was able to work the fish tape up the pillar to the antenna opening, then attach the new antenna connector and pull it back through. Hook it all up, screw it in, replace the foam, and I was done. The fishing part was harder than I thought, though.