[Distutils] pip and PEP 517 Backends

I have a PEP 517 compatible backend which works with pip to install from an sdist (via an internal wheel). However there are a couple of issues... pip swallows all output from the backend. Is there anyway for the user to see the output (builds can take several minutes)? I would like to pass options from the pip command line to the backend but neither --global-option or --install-option have any effect (the config_settings argument is always None). How do I achieve this? Thanks, Phil