Geoff, how about this...export a 5-second section of the song, unmastered and 32-bits. Open a new project, import that short file and clone it so you've got 3 identical copies. Put separate instances of the limiter on each track and adjust for -8, -12 and -14 respectively. Adjust each track's volume so that they're all at the same subjective loudness when played back.
Now you've got a demonstration that most people will never have the opportunity to hear: the same material mastered to different standards. With the right song, I'll bet this will make dub's loudness-war lesson brief and persuasive.