A glass cleaner with ammonia will work wonders for pulling out coke, coffee, and tea stains. Get a wet/dry vac or a carpet cleaning machine to pull as much liquid out of the seat as you can... wet the entire area with glass cleaner. Let it sit for about 5-10 minutes... suck it out... let it dry (you can use baking soda to speed the process and wick more moisture out)...vacuum... check for stain... if the stain is still there... repeat.
Just wanted to give a little update. The stain is pretty much non existent at this point. A local detailed gave me a top to use dish soap with warm water, rub it in a let it dry and repeat as necessary. The seat however is now slightly darker than it was before in that area but very hard to notice.
Thinking about trying a hot steamer vacuum to restore the color?