There's no universal mechanism for doing this. MEF components 'configure themselves' - there's no external place to select between different implementations except via the catalogs.
The recommended approach in this case is to use ImportMany and select the implementation based on metadata.
You might instead consider either filtering the catalog or filtering the types that go into the catalog.
Another option is to set up a custom container topology - the ExportProviders passed to the constructor are checked in order and any ExactlyOne imports will be resolved by the first ExportProvider that supplies the part.