Different account, but OP here. (I've lost my password for the original account, and evidently HN does not have a password reset function.) For what it's worth

Different account, but OP here. (I've lost my password for the original account, and evidently HN does not have a password reset function.) For what it's worth, for the time being I've gone with a prominent ajaxy Feedback "drawer" in the lower right corner of every page: a bit of text and a form by which users can send us a message. Similar but not quite the same as the User Voice tabs. When closed, the drawer simply says "Feedback?" in big, yellow on red letters. When open, the copy is describes the site as a "sneak preview release". Hopefully this is prominent enough that users will see the message at one point or another, but without introducing a gateway, splash or interstitial page.