Whilst I have never done it, as I live here, GVA seems to be an ideal place for a turnaround. BA planes always seem to be docked, so no buses. You get off the plane, go down two flights of stairs, do an about-turn, leaving the rest of the arriving passengers, go up one flight of stairs and you're back in the departure gate area. No security, no immigration. It must be absolutely impossible to miss the returning flight as it's no more than 1 minute from leaving the plane to being back at the gate.
There's a good choice of flights, 9/10 per day and it's usually a little cheaper than ZRH because the taxes are lower (it's also considered to be an EU airport because of the French sector). The BA lounge is a good long way from the gate, the other side of immigration and back in the main terminal, so not accessible on a direct turnaround.