Do we really want to enshrine shadowing the encodings module as the one true way to do this kind of thing?

Although I guess defining a way to do it properly would be a fairly major undertaking, so perhaps blessing the encodings hack is the practical way forward...

If we do that, I'd like to see a devguide patch that better explains how to generate your own coverage data for the stdlib with coverage.py, the encodings hack and the standard library coverage option.