Cuse and Lindelof explained it in the bonus feature on the Season 3 DVD's:
Damon Lindelof: "We can say that the Others are responsible for bringing Cooper to the Island."
Carlton Cuse: "Yes, they staged an auto accident and he was taken into an ambulance, and he was drugged and he woke up, and he was on the Island and … so that was true. They did get him there."
I wonder what they would've done if he asked for Helen? Or some running shoes? Or a pizza?