I had a similar problem flying from HAM (Bermuda) to LHR via JFK, I landed into JFK at 13:00 and the flight to LHR wasn`t untill 22:00 so I decided to go into the city for the afternoon, I put down the address of the Waldorf Astoria hotel in New York, and said I was here on vacation and was leaving the next day.

I have been into the U.S about 14 times now and the only questions I have been asked are Where are you staying (one location or touring)? Are you here on business or vacation? How long do you intend to stay?
I haven`t ever been asked to produce evidence of my return ticket, after all you may have an open ended or flexible ticket (as long as you leave within 90days under the visa waiver program) and as far as I am aware your first night`s stay needn`t be pre-booked, again I have never been asked to provide actual evidence of a confirmed hotel reservation.