I personally tend to leave others alone (by default) who I see doing this and try to come back another time. When I check for days and they keep on and on and on at it without breaks (again, literally for DAYS)...I eventually message them from an alt explaining it's obvious what they are doing and that they are abusing it to monopolize the area preventing others from playing. In that message I wish them the best, explain I'm only trying to help them as they probably didn't stop to think how obvious their actions are. If that doesn't work, by the follow morning I start reporting them until I see their characters removed from the zone.
At that point, I figure if they don't give a crap about being banned or how their actions affect the MQ community as a whole...I don't feel bad about finally reporting it.
I wouldn't be against perhaps
training
them, but I've heard of cases in the past where the person doing the training gets reported back...no matter how justified they may have been. Even if nothing would come of that report, I try to avoid getting ANY reports on my account if I can help it. I like the idea of streaming it online as an_image suggests in this thread, that's creative. Another option I've seen others take is to blast them in general chat hoping others will be curious enough to come report/witness it...but that is rather dramatic and most people there won't care. It also doesn't do any favors to the MQ community to make such a public spectacle out of it.
My suggestion would be to be patient at first, but if it persists for more than a day or so (without any breaks) you should send the person a message from an anonymous alt explaining how obvious their behavior is...and that they should consider giving others a chance at the spot since their toons stay logged in 24/7 and never log out for sleep. 24 hours later, if they haven't changed a thing...100% report them. MOST MQ users will avoid that type of confrontation and share zones/camps and be super polite to prevent problems. When you find someone who takes over zones like you describe for days on end...they absolutely deserve whatever is coming to them. They are begging for it.