This might sound silly to some of you...but I had a similar problem with my hunting coat a few years ago. Dumb cat.
Anyway, try laying it out on your lawn directly on the green grass. I know...I know...I thought the same thing when my wise old mother told me to do it. But I did it anyway, and after two days, it was basically scent free. She said it was a trick she learned from an old lady farmer in Missouri about the time I was born....
Not sure what happens, but I imagine it has something to do with the gas that is produced through photosynthesis.
Did you try any brand name scent killing sprays?