Contrary to popular belief, you do not need a return/onward ticket to apply for entry
Where are you getting that information? Customs and Border Protection says
>At the time of application for admission, a VWP applicant must:
Be in possession of a round-trip ticket that will transport the individual out of the United States to any other foreign port or place as long as the trip does not terminate in contiguous territory or an adjacent Island; except that the round trip ticket may transport the traveler to contiguous territory or an adjacent Island, if the traveler is a resident of the country of destination or if arriving at a land border, provide evidence of financial solvency and a domicile abroad to which the traveler intends to return.
The State Dept. says
> [You may be eligible for VWP travel if you can answer “YES”]
>If arriving by air or sea, are you traveling on an approved carrier and do you have a return ticket abroad?
>Travelers with onward tickets terminating in Mexico, Canada, Bermuda, or the Caribbean Islands
must be legal permanent residents of those areas.