This is not a good idea. The sterilization process used on hypodermic needles is gamma irradiation, a much more powerful, for lack of a better term, form of sterilization than alcohol. Alcohol doesn't kill everything, certain molds for instance, and you're more likely to contaminate the needle with fibers than you are to remove any possible contaminants. There's a reason that the proper injection technique involves swabbing the skin (for at least 15 seconds, which means you'd need to wipe your needle for the same amount of time to see any theoretical benefit) and not the needle. You're also removing the coating on the needle, making for more drag and a possibly a more painful injection. Do as you wish, just letting you know you're potentially causing more issues than you're solving.