New patch, new gear, new soloings :)
Did it with 526 ilvl gear, but 520+ should be more than enough if you use two Heroisms.
Thankfully, he didn't hit harder on Heroic, and the increased damage from his DoT was compensated by the fact he doesn't melee during world in flames. Using dire beast for pet rez also helped. The full guide can be found here:
To put it short: Phases 1, 2 and 3 weren't harder than on normal, so it only was a matter of mastering the transitions and phase 4. A pretty good fight, since many attacks deal 500K damage so some mistakes were still prohibited, but rng isn't an issue. Definitely my favorite cataclysm boss both for raiding and soloing.