Because I hate to waste even a drop of expensive FOs, when I'm ready to throw away an "empty"bottle, I know there are always a couple of drops left, so I turn the bottles upside down on a paper towel to let every last drop drain out.
What a great idea! I also hate wasting anything, even the drops of FO that won't come out of the bottles, so I took your idea a step further. BB sells something called Nature Fix. It's an inexpensive blend of corn grit and cellulose fiber that is used in potpourri as a fragrance fixative. I put a couple of teaspoons of that into an empty FO jar, shook it up, and let it sit for an hour to really soak up those drops. Then I poured that into a little organza bag and tied it onto my rearview mirror. My car smells amazing and the fragrance really lasts. Now I have a use for all those empty/not-really-empty FO jars that were waiting to be washed out! Win-win!