Actually this method was indeed posted awhile ago on these forums, the problem is it's not really feasible due to the time spent positioning alts, the fact that it only works so far from the instance portal, and it requires a specific class(warlock, maybe boomkin but that's risky), and most of the time if you don't do it right or have resists(even Critters can resist lv70s) you're gonna be in trouble, not to mention if your alts get attacked, they're most likely going to instantly die on contact :p