Take an old drill bit and chuck it upside down in a drill press. Make sure the bottom is flat. Put your drill press to the fastest speed it can go. Put the metal you want to spot anneal under the drill and press down while running at full speed. You will need to clamp it. Press fairly hard to create friction and heat things up. It doesn't take that long to get pretty hot in that spot and soften it up. The drill bit is ruined but you get to save the blade. I've had to do this a couple times. Now I just use a carbide drill but if you don't have one in the size you need, I know this process works.