How would someone noticing the paddle boat be unaware that the girls were not alive? If unconscious or dead, they couldn't sit up. If they were slumped over or lying in the boat, that would be very noticeable, IMO. From my understanding, those boats are pretty shallow, not much room for more than two people, maybe four, and no place to conceal one body much less two. And they move very, very slowly. That would be the last mode of transportation a pedophile would think of using for getting their bodies from one point to another, not to mention a lot of work, IMO. IF they were in a paddle boat with someone, I would have to believe they were still alive. If they were not alive, then why didn't the perp just dump them in the water?
I don't believe LE thinks the girls were ever in a paddle boat... I think they were hoping that whoever took that person's boat may have possibly seen something as he/she was in the boat. If they thought that was the means of transporting the girls from one place to another, then I don't think their request would have been so casually stated. JMO, of course, and while anything is possible, I can't buy your theory. Sorry.