not pull the lever, roll the guy on the one track over so he's with the five and now it's six, then lay down and make it seven, then release the trolley.
While looking for this video i also saw that the same dude made a video 4 years later with the first kids younger sister. She had a slightly different solution:
https://www.youtube.com/watch?v=ZULuedsaB9U
Derail the train.
Return to freakin sender!
There's another trolley coming, and she's trying to stop it from running over people again by crashing the first trolley into it.