On Monk, you can keep stacks through the jumps, stay as close to the middle as you feel comfortable with (obviously you don't want him dropping on your head though) and start running to him as soon as he hits the ground and attack from the front for a few hits whilst running to attack position. BUT there is a slight extra delay in the heart one so you lose it there, but should be saving perfect balance for that one. At the end of heart you can -sometimes- keep it depending on how quickly the second gaol gets taken down (the slower the better, but this is dangerous.. for the person in the gaol anyway

). Of course, if you get gaoled then you are losing stacks unless your party is very very fast at getting you out, but if it's first gaol on heart no chance. Bombs/weights/landslides shouldn't require you losing stacks, although sometimes you have to take a few risks to keep them. Like fighting on his foot for the cross pattern bombs (the happy place bombs :P).
If GL3 got 3-6 more seconds, it's quite likely you could your stacks for the whole fight (excluding bad luck on the first heart gaol), so I hope that is one of the changes (not sure if it's been confirmed though).
But I have to say, even in near full ilvl90, and not losing GL3 except at start and end of heart, I can't seem to match the blms in my FC for overall damage in this fight... although in heart phase, by popping all cooldowns and oGCDs, I can often come close for that specific target.