Sorry to be a naysayer, but I don't think there's anything you can do to keep such a large piece of end cut from splitting, and badly. The wood must eventually dry to equilibrium with its surroundings no matter how much you slow the process. When it does eventually dry, the wood shrinks in the tangential direction about twice as much as it does in the radial direction. That's just too much shrinkage to be accommodated without cracking an end cut much larger than an iced tea coaster.
“We should be careful to get out of an experience only the wisdom that is in it and stop there lest we be like the cat that sits down on a hot stove lid. She will never sit down on a hot stove lid again and that is well but also she will never sit down on a cold one anymore.” - Mark Twain