From a practical viewpoint, ending at the point of origin is academic as long as you have an extra segment remaining when you get to where you really want to end. Just book but do not fly the final flight back to your point of origin. While it is true that they then have the legal right to charge you the difference between what you paid and regular fares on the point-to-point flights you actually flew, this has been discussed numerous times here on FT in the past and no one has ever reported that it has happened.