MaddLlama
But, I think a good place to start is to create Pagan "centers" - buildings, with private natural land on its property when possible, to be used for several purposes. As a community center type place for Pagans, it wouldn't necessarily try to promote a particular creed (outside of any necessary generalizations to inform people of what exactly it is), but be more of a central place to teach, and to hold gatherings. Sort of like the YMCA for Pagans. It's not really an institution, but it's a baby step.
Centers would be awesome. You can have a center without having to nail down really rigid structures; it basically becomes a resource that those interested in what it has to offer can draw upon.
I was considering recently that having at least some sort of way of communicating with each other is in effect a sort of 'organization' albeit a loose one. Without that, the headstone campaign would have fizzled out before it ever got started. I think that being able to come together as a group for certain things, particularly legal rights, is really important. Otherwise we won't be heard and we won't get the legal rights we deserve.