Hi, Russ. No, I don't have the notion of private-to-you airports. I actually don't want to have such a feature, for the exact same reason that I don't want private-to-you aircraft: crowd-sourcing of data depends on people creating shared data. If it's private, then the crowd-sourcing will fail.
But there is absolutely nothing wrong with making up codes for your friend's farm and using that. I generally suggest 5- or 6- letter/number codes, so as to avoid naming conflicts with ICAO, FAA, and IATA codes, but go ahead and give that sand bar or field a name. And then, yes, autodetection will work (once the airport database update migrates to the iOS/Android device, which usually takes a few months...)