I don't know how to trigger it, personally, but I have had thoughts on how to do it.
Make yourself a dummy spell (ability that doesn't do anything) and trigger it so the unit hit by the ability is swapped to Neutral Passive, give it the Wander ability (the one critters have) for the duration of the spell, then hand it back to the original owner.
Should be possible, though I haven't tried it yet.
Create a new ability based on Tornado Wander. Change the Cast Range/Area of Effect, add it to the unit and turn on its collision (adding Tornado Wander to a unit turns it automatically off). After X seconds simply remove it. That's all.