Can you preserve zest?
I've successfully frozen yuzu (a Japanese citrus fruit slightly similar to lemon or grapefruit) zest for two or three months without much damage; the flavor isn't perfect, but it's usable as long as you don't get serious freezer burn. I've kept it in a small Rubbermaid container. There is a potential problem because citrus oils can damage certain types of plastic over time, but this didn't affect me; however, plastic bags won't work so well.