In that case you can do a Show HN. The guidelines are only trying to prevent Show HNs for things that can't be used yet. If you want specific advice, you're welcome to email hn@ycombinator.com. (That goes for anybody.)
We might need to relax this rule. Good work can get off the ground in many ways. Drew Houston got initial traction for Dropbox with a video rather than with working software. Our intention isn't to be overly strict—it's mostly to detach "Show HN" from vaporware landing pages and market tests that don't have serious work behind them.
I was about to release signups for a private beta of my current project, but apparently that no longer fits the formal criteria of "Show HN."
Disappointing to say the least.