One day while making cheese, I also wanted to make a batch of yogurt. My problem was that I only had one long-stemmed thermometer, but needed two. My solution was to bend an "S" hook so that one end of it was crosswise to the other. I also opened out one end of it so that the opening is large enough to hook over the edge of a kettle.
Here are a couple of photos. I apologize for the quality, as I'm using a cheapo camera. I hope the pics get the idea across.
The thermometer and altered S hook on my range top:
Putting the thermometer into the hook:
Thermometer hanging on the side of the kettle:
The thing I like about using this method is that I can put a lid on the kettle without having a big gap at the side. The lid rests on top of the S hook easily.