I had the same problem when I EPed, but I was so paranoid and afraid I was going to lose my milk supply entirely. I ended up donating milk, about 10,000 ounces. I finally slowed down and stopped pumping when I was pregnant since that pretty much killed my supply. Sorry I don't have better advice.
- When you decrease the frequency of feedings, you said your breast become very full and engorged. If they become too sore you can hand express just enough to relieve the engorgement. It is important to let your body know your baby does need that much milk, and the way to tell it is by not emptying your breasts.
-When you pumped more frequently for shorter sessions, it likely increased your supply, so stop that. :)
-I agree with PP that you should look into donating milk. Here is a link for the Human Milk Banking Association of North America
-Don't decrease your supply so much that when you are able to bf your LO you have low supply issues. It's better (IMO) to have a surplus of milk that you can donate than try to increase your supply later.
Lastly, hang in there! :hug It sounds like you're doing great!!!