-n't infixation in English

Consider the following word:

Finally one said "It's astonishing. Frankly astonishing. The man has actually got charisn'tma."
"Your meaning?"
"I mean he's so dreadful he fascinates people. Like those stories he was telling... Did you notice how people kept encouraging him because they couldn't actually believe anyone would tell jokes like that in mixed company?" - Terry Pratchett, Feet of Clay, 1996, p. 289

This word may not be original to Terry Pratchett, incidentally - this document suggests it appeared in a show called My Word! back in 1976. It gets 90 ghits, (including one in Polish), concentrated disproportionately in reviews:
* "...cardboardy Paul Walker, whose lack of presence ('charisn'tma'?) sucked much of the life out of..."
* "Collectively, they exude charisn'tma, and one or two even possess what Ken Campbell once described as "the legendary Minus Quality" whereby when they exit, the stage somehow seems fuller."
* "Hard-edged r&b from the band with a front man who exudes charisma. Me? I exude charisn'tma."

In this structure, a common word's meaning is "inverted" for comic effect by adding -n't to a portion of it which resembles a common auxiliary verb. I can think of at least one other such case:

"I even attempted a beehive do, but I ran out of hairspray. So it kind of turned into a don't." - Douglas Coupland, Generation X, p. 82

Believe it or not, this one gets some ghits as well, though it's obviously hard to determine how many:
* "Scarlett's Hair-Don't"
* "Hair-Bow is a Hair-Don't"
* "Is it a hair DO or hair DON'T???"
and an entry in the Urban Dictionary.

And at the even less lexicalised end of the spectrum, we find stuff like this:
* "Another Republican’t paragon of virtue"
* "As it happens, my friend Tom Schaller noticed that many of you liked “Republican’ts” — and he suggests that we all start using it, at least as often as the GOP throws around “Democrat Party.”"
* "You’ve seen me in action. You know I’ll get you out. I’m a Mexican, not a Mexican’t!”"
* "did you hear about the lazy, unambitious bird? It was a whippoorwon't. (Yuck, I hate puns.)"

Your question for 10 points: do portmanteau words like this need to be accounted for by a full theory of morphology, or are they monstrosities that should be swept under the rug into psychologists' labs? These words' two components seem to both contribute to their meaning, but not exhaustively, in much the same way as the meaning of "catty" is partly but not completely predictable from "cat" and "-y"; how should that relation be characterised?