Hey there.
I am currently doing this with my wizard WITHOUT Firewalkers. I manages to gather 6 spawners.
I only use Shock Pulse for killing the rats by Aming AWAY from them (into the wall). It kills them very fast but does not hit the spawners.
Be use to have ZERO area dmg and Thorns!
Since i am attacking constantly you wont get a DC because of inactivity!
Edit: the rats seem to only drop gold until now. Can someone confirm item drops without threatening shout?