The Lake is about as close to the school as the Maze, why not turn the Gillyweed (in the film) or something else (in the book) into the portkey and give it to Harry then?
The concept remains the same, just rephrased as 'Barty Crouch should have turned other object into portkey' - but I get your point, original question could have been rephrased more clearly to avoid confusion
edprince
