The Copenhagen Metro runs all day and all night, so it's pretty easy to find an empty or almost empty train -- near the end of a line at 3am on Tuesday should work.

The scenario certainly also works for trains in general -- perhaps even more so, since an older, manually driven train is less likely to be filled with CCTV cameras linked to a control room. (The metro has this, but it seems they're only monitored once someone presses the emergency button.)