You will have to spend some time with the turkey fan and a decent knife. All of the meat will have to be cut/scraped off of the tail. Turkeys do a lot of preening. Preening requires oil. All of this oil comes from glands in the tail. These oil glands also need to be removed as much as possible. The quills are completely surrounded by a yellow substance that looks like fat, but is actually the oil gland. Again, scrape out as much as possible, the more the better.
Once you have the tail as clean as you can get it, fan out the tail on a large piece of cardboard and pin the feathers down to hold the full fan shape. Completely fill the tail cavity, then cover it completely with Borax. After a day or two, dump off the Borax and repack and cover the tail again with fresh Borax. A couple days later, do this again. After about six days total, the tail should be pretty well dried out and will maintain the fan in the open position. You now have one turkey fan that you can use for a decoy or a wall hanging.
I have "cured" and mounted several dozen turkey fans using this process and it works. Just takes a bit of time and patience. Good luck.