Forgot about holding down the mouse button. Yes that should work.
Unfortunately, since all he can access is Mousing Around, once he's in it, it cannot be quit except for turning off the Mac. And no, Cmd+E won't work either. I don't believe it can be done from the main launch screen either, since the Finder has been substituted with the special MGT Finder which does not enable all the normal Finder commands. Only when clicking Let me use My Macintosh is the real Finder loaded, but this FInder is a beta version as well, so not sure if all v1.0 Finder commands are included there either.