bo'Dagh'a'vetlh Dalo'nISbe'. That phrasing is fine (it's just not intended to be a literal translation) and I would say so even if it had never appeared on screen. I also don't see a problem with bIvoqbe' 'ej muSuj. The fact that you can't use 'e' as a subject doesn't mean there's no way to refer to a previous utterance as the subject. It just means you can't use 'e' to do it. Words like ghu'vam or ngoDvam are one option. The example of Do'Ha' suggests you can also do it with just an unstated third-person subject.