> Alternatively, if I have a username "not_godelski" then how do I get in contact with someone on HN while maintaining anonymity?

You can't, and I don't think that's a surprising outcome. If you have a non-anonymous identity on one platform, and link it to your anonymous identity on another, then that latter identity is no longer anonymous.

You just can't really mix your anonymous and non-anonymous worlds without de-anonymizing the latter. That's kinda a fundamental property of how anonymity works, isn't it?