Just push them in front of the train.
Unless it's the one with the weird glass barrier thing that the train has to line up perfectly with. That confused me the first time.
( BraynDedd Natasha Kaplinsky's labia majora, Thu 9 Jun 2011, 9:41, archived)

They only run up when the train arrives, so I can only push them into the train, not under it,
but it's a nice though.
( Zuowan, Thu 9 Jun 2011, 9:44, archived)