Been doing this myself. Have a friend I always use to play with, he single box and I quad box. We created an alt team just for some fun, me 3 warlocks and he 1 mage (1 spot for our booster paladin)
We have same name, with ascii chars, and the exact same look & gear. Sometimes I send my locks to follow him and everyone think he is the multiboxer.

We are soon lvl 40, and I'm confident that GM's can see that it's not 1 person playing all 4 chars.