I've done it but only when it was used as a primary with good headspace. So if it's up to the neck you won't be able to add your priming sugar without it over flowing.
What I would do (just thoughts...) is siphon out a bottle or 2, set them aside, add boiled priming sugar, swirl with the siphon gently a bit, just enough to mix it around. Continue to bottle the rest and then bottle prime the first couple I set aside.
Orr if you have a spare carboy you can what above said, and do whatever with what didn't fit from the added volume of priming sugar. ACTUALLY, you'd be losing the bottom trub from racking, so I doubt you'd have any leftover.