There's no way to do this. If you found one, it would be a security issue and would be fixed, because if an attacker could silently force-switch a user from the sandboxed PPAPI plugin to the unrestricted NPAPI plugin, then the whole security benefit of having a sandboxed plugin would be lost.
(And hopefully your tutorial is pointing out to users that following your instructions increases their vulnerability to attacks from malicious websites, so that they are making an informed decision.)