Has anyone done this? I have found the AlphaVSS project on Codeplex, but is stops short of providing a way to implement a writer.
Like the AlphaVSS page mentions, the VSS APIs are not a real COM API (and therefore are not useable via COM interop). They are just C++ APIs that sort of look like COM. So it's of little use to pure managed code. You need some kind of C++ wrapper or shim regardless what you want to do.