Suggestions to remove smoke odor from headphones?

Why don't you give roomSHOCKER a try. I haven't used it personally but I've read great things about it.

"Cigarette Odors. That residual smoke odor that you smell is what scientists now call "third-hand smoke," that tarry, smelly residue left behind after a smoker has smoked in the room. Our roomSHOCKER attacks many of the organic molecules in Thirdhand Smoke (3HS), oxidizing them and eliminating the gasses and odors that they emit. Most of our competitors merely mask (with perfumes) or encapsulate (with waxes) the 3HS molecules, which means that they are still active and dangerous. Adding a perfume to the dangerous 3HS gasses doesn't make them less dangerous -- it just makes you less aware of the danger!"

Try to leave them outside in a windy but not sunny and neither humid place for a day or two?
If it still smells, standard methods to clean leather work pretty well, you can google them quite easily.

If a university or business near you has an ozone chamber, that will likely do it.

Or you could just take up smoking.  :D

First you need a large box, bag or similar. Fill up a bowl with vinegar, then place the bowl and headphone in the box and let it stay overnight.

Repeat if needed.

you might want to try an use non sudsy ammonia, the clear stuff not the yellow lemon scented stuff. this is the only cleaner that really gets smoke out of anything and everything. i have washed cloth Senn pads in hot water with Ammonia before with no damage to the pad itself, its actually pretty amazing how it works so well. if it bugs you that much you probably would want to fill a sink with water a few caps of ammonia, dip the pad in and sqeeze it a few times, rinse it with water then dry them quickly. after use some Lexol leather stuff to protect them. if you keep them in a case try cutting up the pine tree car air freshener in small pieces and keep a few in the case just to lightly cover the smell until you and the headphones adjust..

i think thats your best bet but in the end you will never get all the smell out nomatter what you do and how long you wait.