PFA the patch. It's short but I think it mitigates the problem.
I took a look at where these options are discussed in the documentation and now feel that we should make these options clear more broadly (config and libpq, plus pointing to --name from -c in a couple of places). It doesn't add much verbosity and, frankly, if I was to pick one "--name=value" would win and so I'd rather document it, leaving -c alone for historical reasons.
I've attached a replacement patch with the additional changes.
And I just saw one more apparently undocumented requirement (or a typo)
You must specify the --config-file
The actual parameter is "config_file", so apparently we are supposed to either convert underscores to hyphens or we have a typo.