What I used to do, when the guy lit up, especially without seriously asking:
Stay relaxed.
Do everything according to the book.
Look out to your right window.
Open up the air outlet near your right knee (the 732, 733 etc. had one there) all the way.
Without even looking at him, point the airstream right in his face, so that he gets the ashes all over him or even blow the cig out of his face.
Act like you didnīt even notice he was smoking, should he start complaining...
or:
Go and take a pee every time he starts to smoke....