The only way to stop movement, is by using a movement key.
So hit W or S or one of the arrow keys.

I was doing the collect the fires quests with my team.
There was a flagged horde priest already there.
I was happy enough to gather the flame and not roast his ass there.

He decides to run into the midst of my now-flagged group and fear me.
I had dropped my first totems in the totem stomp macro.
So I had: Totem of Wrath, Tremor Totem, Mana Spring Totem and Healing Stream Totems down.

The Tremor pulsed about two seconds after the fear.
My slave shammies use target=targettarget, but my pally already had the priest targeted.
I clicked my assist macro (mouse thumb button) and my interact keybind (other mouse thumb button).
Then pressed my W key to break the movement.

Then it was a couple of seconds for 4x Flame Shock, 4x Lava Burst.

Interact works great with casters.
It turned my entire team towards my target.