The park immediately established maximum guest capacities, so it would never happen again. When you're riding the Mark Twain, look up in the wheelhouse, and you might see a guest piloting you. You can go up there too. If you're already aboard, simply knock on the wheelhouse door and tell the Captain how many you have. If there is no one else up there, you will be let in.
Captains enjoy the view from up there, but it gets lonely riding around and around all day.
Many of them enjoy the company, and you'll be rewarded with a certificate attesting to the fact that you are a licensed riverboat pilot, good for one year. You'll also get to see a few old time pictures of Walt and Admiral Fowler, too. Fantasyland Sleeping Beauty's castle has 22K gold-plated spires, but, when Walt wanted to plate them, Roy, the money man, objected. Walt sent him on a business trip and had the work done while he was gone, but you'll notice that one of the spires has been left unplated. Walt did that deliberately, in keeping with his quote that Disneyland will never be completed as long as there was imagination left in the world.