Otherwise, you could put a comma, anywhere in a sentence and argue, that that's, where a pause in speech would go if you were saying it.

I mean, if I were transcribing Christopher Walken or William Shatner, yes, I may type it like that. Sometimes ungrammatical things add to the understanding and/or character of a sentence.

Although personally, when it comes to denoting trailing off mid-sentence I'm partial to the ellipsis.