I have just released the initial version of my new open source project which is designed to allow one set of integration tests to run against in-memory fakes and against a "real" repository using only pre-compiler directives.
This is useful when you have a suite of SpecFlow tests that you want to quickly run locally whilst developing (e.g. with NCrunch) and on a cloud build server (e.g. GitHub) where you don't always want to hit "real" data resources, but want the flexibility of occasionally switching to "real data mode" and running the same set of tests against a real MongoDB or SQL server (for example).
The initial version has one backing store implementation, for MongoDB, but I'm hoping by making this open source other backing stores can be added over time.
You can read more about it on the GitHub page here: