Hmm, good question.
I think with the example you gave, the words can both be capitalized like one-word sentences, as they're real words. The trouble happens with a syllable breakdown (not an official term; I'm just trying to explain what I'm seeing) where not everything is a full word. E.g. Non. Committal.
It seems to behave a little like an infix, where a word is interrupted by another word, usually a swear or a PG equivalent, e.g. unbe-*******-lievable. For an infix, I would suggest either hyphens like I used, or maybe smashing it all together, e.g. unbefuckinglievable. But I think the hyphens make it easier to read.
But I don't think there's a hard and fast rule for infixes, which are exactly what they sound like: the equivalent of a prefix or a suffix, but thrown in the middle of a word.
About the only "rule" there is for infixes is they seem to go after 1 or 2 syllables and (maybe) before at least 2 syllables. But this is a rough "rule".
The reason why I am tangenting into infixes is because they serve a similar purpose-- to add emphasis in the middle of a word.
I suspect that there's no actual name for this yet. Technically, it's not even Interrupted dialogue, which would be handled with an emdash, then closing quotation marks, line break, and then the interruption--- because in this instance, the interruption isn't coming from anyone or anything external to the speaker. The speaker is deliberately creating the interruption.
I suppose this is a very long and roundabout way of saying that I have no idea. But if I was tasked with creating a rule for this and naming it, then this is the sort of logic I would use.
Un. Helpful. -- I know.