I was looking in the forums to see if there was another post with this but I only find this one maximize-invincibles-reins-farming-icc-25-heroic (Maximize Invincible's Reins farming in ICC 25 Heroic!).
I found today than you can get to LK 25HM without clearing the whole instance in that difficulty. What to do:
1.- Clear the first 11 bosses en 10Normal (you can solo this without too much trouble).
2.- Leave the instance.
3.- Switch the difficulty to 25Normal.
4.- Enter the instance.
5.- Swith the difficulty to 25HC.
6.- Go to the LK Throne and PEW PEW
Why I think this is an exploit? Because you are supposed to clear the first 11 bosses on HC to be able to pull the LK on HC, if you don't clear all the Throne should be empty.
P.S.: Sorry about my poor english