You won't suffocate if you don't add (breathe). And you can't dictate what your breathing pattern and rhythm will be by that point. If you struggle with this, practice the presentation speaking on the exhale. The moment you feel yourself breathless, stop and inhale for 2-3 seconds. Considering the shame we attach to our stutter, a few second silence as you inhale is ought to be imperceptible and less embarrassing than the stutter, right?