Yeah-- oddly, my DD has never been a read-aloud kid, either. I know exactly what you mean about not having an auditory beacon to follow!! She did the echolalia-like thing, too-- from everything around her-- movies, TV, radio, conversations. It was really creepy, but there was something about her intonation that would "shift" slightly when she was using whole chunks from elsewhere. I always knew-- but I was the only one who knew that it was 'borrowed' content that she was trying out. She usually managed to place it completely appropriately contextually, so people other than me didn't understand that she was quoting Emeril rather than making it up as she went. It wasn't exactly echolalia, either, because as noted, she was using it IN context. It was almost like a word-acquisition skill on steroids. She acquired whole phrases or paragraphs and used them. It gradually stopped when she was about five or six.

Schrödinger's cat walks into a bar. And doesn't.