If the ticket is booked using a U.K. credit card and billing address and the return leg is several months after the originating leg, the chance the airline will try to track you down in the U.S. seems very slim indeed. People change travel plans all the time.

As far as CBP is concerned, the only thing they care about is your intent to make America your permanent home. You are otherwise free to come and go as you please -- if questioned you can always say the one-way tickets were too expensive and you will decide later whether to pop back for a quick visit to the U.K. to see friends or throw away the return leg.