I do think is possible to do ONE park under the right conditions. I played around with Ridemax using the slowest day I could find (Jan 17 2013). I assumed early entry and doing ALL of Fantasy Land in the early entry hour. Ridemax was able to make a plan to fit all but the tree houses and Tom Sawyer island. Ridemax was not able to make a plan fit on other days I tried despite much longer hours.
When I went to Disneyland in 2010, I rode every ride at least once over 1 1/2 days. It was odd the second day when I realized I had been on everything there was! It's like those things you dream about, but never expect to have happen.