I've gotten the temp to hold steady around 99 degrees by raising the metal rack a bit higher over the cooler with egg carton supports. I have no idea what the humidity might be. The egg is wrapped in a washcloth that is still damp, and there is also a bowl of water in the bottom of the cooler. It's in the air-conditioned house (about 79 degrees) in a corner that doesn't get the hot afternoon sun, so I hope the conditions will hold steady. The gosling is still breathing, I can see the washcloth moving, and sometimes it peeps.
There would be no way to glue this eggshell together, it's like when you have a hard-boiled egg in the shell & it gets squashed. I will just keep watching, try to keep the temp steady, check to be sure the washcloth stays damp. I'm hoping that in a few days it will absorb its yolk & try to wriggle out of what is left of its shell. I will help if it gets stuck in a too-dry membrane.
Please keep praying for this gosling! I also will set the alarm for early in the morning so I can let the goose out of her pen right at sunup, so she doesn't get frantic & crush any more of her eggs. She has two more in the nest.