When they take into account fair use, they take the entire case into account, rather than following any hard and fast rules saying that using X% is "fair."

In other words, no, there's pretty much no way they'd buy any attempt to game the system so transparently. That's why you need a lawyer.

No, the courts take context into account. So for example, it might be perfectly legal to post 2 sentences from a book on your blog, if 10,000 blog posters conspired to post a different 2 sentences to share the whole book, that would be clearly illegal. Furthermore, the law is interpreted by Judges, who are people, not machines, and they tend to take a very harsh stance against people who try to game the system.

YouTube are just doing a first pass filter. They're not saying that 30s of a work is legally allowed.