I'm afraid not - at least, not using the techniques employed in this add-in. (All the add-in does is flip some bits to disable "actions" associated with the email, and the available actions are forward, reply, reply all and reply to folder; it does not prevent
copying of the email, which is pretty much the starting point for sending it as an attachment.)
If you wanted to prevent this sort of thing, the most robust solution would be to use
IRM, though that is considerably more heavyweight.