I realise there is a risk, but I'm only doing it once. I recall the old days, like some other members, when you could legitimately get a ticket issued somewhere cheap, and not use the first or last leg. I think it depended on the currency in which the ticket was issued.
I had a first class (no business class then), ticket, Lagos/London/NY/Rio/NY/London/Lagos, absurdly cheap. I started and finished in London, no-one minded. They were the old book tickets, you just tore out the First ticket, Lagos/London, and didn't use the last one. Happy days!