Sensitive to Metal - Nickel Allergy

I have a sensitivity to nickel. A lot of the metal in costume jewelry contains nickel because it's fairly cheap. When I shop on Etsy I always search for nickel free earrings, but sometimes even the ones I pick up can make my earlobes start to burn after a few hours. So I'm trying this:

I've heard that if you coat the posts and backs of your earrings in clear nail polish it can really increase the amount of time you can wear the jewelry for daily. Has anyone else had success in doing this? I'll let you know how it goes.