This best works if you are a tank (maybe healer, depending on the que times).
step 1) Que for a random heroic and enter it
step 2) if its the heroic you want yay. if not
step 3) teleport out of the dungeon and tell the ground you will be afk for whatever amount of
time (i usually say 10-20 mins)
step 4) they kick you and you reque. rinse and repeat until you get into the heroic you want.
This can take some time since it randomly selects the heroic. You also don't have to worry about reque time. since you get kicked the 15 minutes you usually have to wait is wiped.