{Ha'} certainly qualifies as a "first-person imperative" in my book.
I also think {DaH} can help to give an imperative flavor to a phrase
like {maHIv}, either in its normal position at the front of the sentence,
or as a separate adverbial utterance.
{maHIv -- DaH!} sounds to me like it's intended as a command addressed
to the first-person plural. :)
-- ghunchu'wI' 'utlh