It must be absolutely torturous if your nose starts itching and you can't scratch it for several hours, when you're on EVA. How do astronauts deal with it? Are they undergoing a special training, or take some kind of desensitizing drugs? Or apply some special anti-itching cosmetics?
"We have a squishy thing inside we jam our nose into while we clear our ears — we scratch our nose on that."
The "squishy thing" is formally known as a Valsalva device (used by both astronauts and divers for equalizing pressure in their sinuses. (Thanks to Organic Marble's comment).
In addition, astronauts wearing Orlan spacesuits can actually pull their arm inside the suit to freely scratch an itch. See called2voyage's answer to this question as well as this entry on Thomas Reiter's EVA blog.
How about Willpower? Every Soldier learns to stand still at a parade or when they got to pledge loyalty. When I had my inauguration at the Austrian Military forces, we all had to stand still for quite some time (2-3 hours no nose or butt scratching) and it wasn't really a problem. Also, if you're concentrated on something serious (like doing work in a completely hostile environment) it is very likely that this distracts you from any upcoming itching.
According to an audio transcript of the Apollo 17 lunar mission, some astronauts had a Velcro patch somewhere on the inside of the helmet to scratch their nose on.