Well, as gruesome as it sounds, I just cut his head off with the scissors. It was very quick and not messy like it would be with a grown chicken since he was so little. No suffering...very fast.
The little one is in a better place now. When he finally got all the way out of his shell I saw that he was also missing his eyes, which made it a little easier for me to cull him. Thanks for all the support!
So I decided to crack open my last 4 Silkie and Frizzle eggs that hadn't hatched. 3 had died somewhere along the way, but the 4th was alive and peeping when I broke it open. It looked fine, except it's ENTIRE upper beak is missing! Obviously I'm going to have to euthanize it unless someone...