I didnt find a post of this so sorry if it is a repost.
Way1: Que opp for random HC. At 3 sec you accept it and DC right after.(It will only work if all accept) Now you should have HS even if your HS is at CD.
Way2: Go inside any instance que opp for random BG, when it pops press enter battle and press then DC right after. Now you should have HSed even if your HS is at CD.
Your HS will ALWAYS get 30 min CD even if it are on CD alleredy
EDIT: You will get the 30 min CD when random HC but no CD when random BG. So if your alliance like me and you get instant BGs you get alot of free HS`s