I think part of the idea is to basically acknowledge the sensation of itchiness, notice it, "observe" it, and then "let go" of it.

Of course, easier said than done. And no idea about the throat thing. Rather than actively trying to regulate your breathing, just sit and try to observe your breathing and let it regulate itself? (ie, feel all the sensations relevant to inhalation and exhalation. Flow of air, etc etc).

Though, to be fair, I've only tried to on and off. And yes, itchiness is annoying, even given all of the above. :)