As you've noted you can't do wet or fermented feed in a gravity feeder. It has to be in some sort of more open container.Dampening the food worked. The crumbled break apart and become like a dough and they are going nuts at it. The volume increases quite a bit as well, but now it doesn't want to go down the gravity container part. I Found these hanging troughs that look like they would be ideal.
I use ceramic cat food bowls (pink bowl on bricks below), small pie plates, ramekins. Anything that's easy to clean and with some weight so they don't easily get knocked over. I don't have an issue with chicks trying to walk in it so "mess" isn't really a problem, and I don't have waste issues as I only put out enough FF to last them the morning and any FF thrown about the chickens will clean up during the day.
For the rest of the day they have a dry gravity feeder as well and any dust/powder left over from that can be made into wet feed, so that entirely eliminates waste.
I don't do a long or complicated fermentation. It's just feed and "enough water" in a single jar and I can keep it going like that for months.
Newly added feed and water:
24 hours later I start serving: