Yes, it is indeed possible to start in Zurich. I was able to price out a fare. However, this takes away the possibility to end in IST (as you pointed out that the destination then has to be a city served by KL and not AF). I was able to construct ZRH-CDG-SVO-IKT-SVO-CDG-AMS-SVG-AMS-CDG-TLV-CDG-ZRH. I'm not sure if more is possible.