Of course, my concept would necessitate losing one of the coolest shots in a movie I've ever seen, but oh well.
Following the same logic, I would do the "three times it drops" scene something like this:
They come to the first waterfall, and go over it without a scratch arriving at a nice river with overhanging tree branches, with Mutt quipping "That wasn't so bad, was it?" (callback to TOD). But then they see up ahead a bunch of falls that will definitely kill them.
Unable to steer the duck, Indy comes up with a daring plan. He takes out his whip, snaps it onto a overhanging branch, and tells everyone to grab onto the whip as hard as they can and don't let go. When it goes taut, all of them are dragged out of the duck just before it goes over another fall and blows into pieces.
Our heroes keep holding onto the whip, which is rapidly tearing apart, and the current threatens to pull them all with. Finally, Mac screams something like, "Bloody hell with this!", and shoots the whip to let them all go, and they fly over the fall screaming. They all wash up on shore, lucky to be alive, and Indy rounds on Mac, who shrugs and slyly says, "Sometimes you gotta make gambles, Jonesy..." Then Ox notices the skull face nearby, and so on.
I can keep going, people.