Doing it right as I type this and this is what we've figured out:
All rogues/mages run north at end of P2, everyone else south, they invis and whatever
When we hit drakes rogues and mages fly north as fast as possible, everyone else dismounts after about two seconds
Maly resets, rogues/mages have drakes in p1.
Drakes CAN be buffed, can get sparks, and can get totems, so they can DPS all during phase 1. We couldn't get the evade bug to work where maly resets and still has full stacks on him, tried about 5 times. Phase 2 the drakes can't target the scions, but they CAN still heal the raid, so if you bring less healers that can keep people up in p1 the drakes can do the work in p2 so everyone can DPS. Unfortunately we're not even close to getting the achievement right yet, we're still figuring stuff out, so I'll make a video of our attempts when we get better at it.
EDIT: Also should have mentioned, we're doing this with three drakes right now, one rogue and two mages, and phase 1 is going kind of slow. We're going to try with more and see if it makes a significant difference, but as of now three drakes during phase one is about as much damage as the players would normally do; the big part is when Maly is flying up for the start of P2 and their dots are still ticking for some extra time.