Always pull the lever after the train passes and move the person to safety. Then repeat

That's how you get free people!

With my new army the process of winning will only acellerate! Next step: world domination

I guess at a certain amount of people, it won't make a difference anymore. If you put 50 or 1000 people on the tracks I wouldn't expect a higher number of fatalities or injuries as the trolley is stopped by the first few victims. Furthermore, it looks like the legs of that box are in the way of the trolley anyhow. So even the folks still in the box might be affected just as much.

Pull enough levers and the train will derail saving the rest.

Borderlands 6: Lever Let Die