Funny this post comes up right now. There I was rained out for two days and searching the internet and just joined a few days ago. So I have not found any yet or placed any, but had the same idea. Here is one that I found while searching the site
http://www.geocaching.com/seek/cache...2-78367ec1189b
As for a helicopter only Geaocache, I was thinking of doing the same thing, but here in Kauai it would be hard for people to get the permits for off airport landings. (We have a few regulatory "issues" that we have to deal with out here.