For this trick you need a flying mount, nothing else.
First get over here:
Then find a Sunfury Warlock, they look like this:
Most of time they have big green demon on their side as in the picture.
Mount your flying mount and fly close enough so you will aggro Warlock from the air:
If his hands glow red, you have succeeded, if they glow in purple light fly to the safe distance.
When you get the red glow, fly quickly some meters up, but not too high so Warlock won't stop casting. When Warlock casts the spell, start flying up, soon you see your caharacter gets damage but spell flies down to the ground below you:
Now the spell will stay on the ground below you if you don't get too close it. I recommend staying in the same height as you were when you bugged the spell, maintaining the height is easiest if you hld right click and press A or D to fly left or right, when doing this you cant fly up or down so it fits this exploit perfectly.
Also, dont fly over ledges while having the spellpet or it will most propably attack you.
I quess you can even take your pet to shattarath if you are patient enough, it is easier with epic mount also. This is a picture of me flying with Spellpet in that smaller alliance city in Shadowmoon Valley:
Same with an epic mount:
To be tested