How do I let linux assign the port that nginx listens on?

This may seem like an odd request but I have a situation where I want to start nginx and let linux assign the port that nginx listens on. I would have thought that listen 0 default_server; would allow this but alas, no.

Is there a way to get nginx to allow linux to assign its port? (And please don't challenge why I want to do this...that's not up for debate :-)

-- Mike Kilian