I tried to see if there's much of a biological difference between passing out and falling asleep, but beyond passing out usually occuring through some sort of trauma once you're out you're out, so it's not that. I've read the book from the moment Cudgeon is tranquilized to try and provide an answer, and unfortunately I don't think there is one, and the whole notion of getting out of the time-stop is pretty shaky so I'm not sure if there's any answer you could construct from the book.
Artemis uses falling asleep to escape the time stop. He bases this plan on that his mother who's in "a narcotic enduced coma", who disappears from her bed once the time-stop is engaged. However, here's the quote from the book on the nature of the time-stop.
Butler frowned. 'What if the humans ... we, that is ... What if we had woken up?'
'Ah yes. Excellent question. The heart of the matter. We wouldn't wake up. That is the nature of the time-stop. Whatever your state of consciousness going in, that's how you stay. You can neither wake up nor fall asleep. You must have noticed the fatigue in your bones these last few hours, yet your mind would not let you sleep.'
Artemis Fowl , Chapter 9
From this, it seems like Artemis's mother should've stayed with them in the time-stop, and the way to get her out of it was to wake her up. "Whatever your state of consciousness going in, that's how you stay". Even if we agree it's possible to cheat this through tranq darts and forcing sleep with drugged champagne, Artemis's mother definitely should've been killed by the bio bomb as she entered the time-stop asleep, and could only have left by being awake. Staying asleep while in a time stop is also the explanation for how San D'Klass delivered presents in one night, so being asleep going in definitely doesn't get you out of a time-stop.
From this inconsistency, I don't think there's any real way to deal with Cudgeon, who is just another inconsistency in the plot. It's a clever idea, but clearly hasn't been thought out all the way through. Cudgeon isn't mentioned again in the story after he's knocked out, so presumably his unconscious body was cleared away with the rest of the operation after they'd left the vicinity of the mansion.