First Get a friend in a car and make him drive next to the ladder after you've climbed on the ladder.
Then if it shows Press B (For XBOX) and O (For PS3) Then get on and make you friend get of and switch to the front seat and drive.
And for the points Headshot a guy or just kill him I think then you get 495 points or something.
You might be invisible when you drive and you will be seen on the ladder.
Its for trolling too. bobo