The size of just a pinky head doesn't intimidate the occasional problem feeder like a whole pinky may. It also exposes the "juicy" brain, which has also been known to stimulate feeding. Scenting a F/T pinky with a lizard is another method to stimulate the reluctant feeder. Sometimes, the movement of a pinky is enough to frighten a hatchling, especially if it is a fairly "large" pinky. Have you tried a really small newborn pinky? It may be hard to find, but worth looking for.
Placing a pinky in the freezer is actually a fairly humane way to euthanize them. They just "go to sleep" when their body temp drops. Because they are so small, this doesn't take long and they don't feel nearly as much pain, nor for as long a time, as when a person suffers from hypothermia.
I would suggest you try the pinky head and/or the lizard scenting, unless you would rather see your snake slowly starve to death. It may, sadly, happen anyway, but you will at least know that you tried all that you could.
I have 8 problem feeders that I am currently working with. I've already lost 5 others. Some hatchlings are just destined not to survive, even with force feeding. 2 of my little "problems" are actually hatchlings that ate their first meal or two, and then just decided to quit. If there hadn't been a delay in their sale, they would now probably be somebody else's problem. Sometimes I'm glad when a deal doesn't go through right away.
And please, rethink your opinion of cornsnakes. Just because you are currently having some bad luck doesn't mean that all cornsnakes are problems. I also breed boas and have 2 more "problems" in that group, and I also lost one of them as well.
Good luck with your little one.