On my return leg from Toronto to Istanbul I noticed that it is possible to upgrade from an economy ticket to Comfort for 280 C$. You just pay the upgrade charge at the TK ticketing counter. This should work even if you have a multi-leg booking since the upgrade charge is only for the single flight.

In regards to hfly's comment about the dimming of the lights, I think you might actually be right that the crew may not have known how to do it because when I mentioned this the stewardess first said that "partial dim of only the overhead lights" was their normal nighttime setting, then after talking to the purser she changed her explanation and said normally they would dim all the lights but that the lighting over the windows were malfunctioning and thus could not be dimmed on this flight. In any case, she said that on future flights they would dim them so I am curious to learn if they are now being dimmed on the return flights from Toronto to IST. Has anyone been on this flight recently?