A similar question has already been answered here: https://stackoverflow.com/a/5307532/1854499
History.js is more of a wrapper for the HTML5 History API, so the answer is the same.
After you've determined which page you'll show when the history state changes (in the statechange
callback), push another _trackPageview
call to the Google Analytics stack like so:
_gaq.push(['_setAccount', 'UA-XXXXXXX-X']);
_gaq.push(['_trackPageview', '/new/content']);
Don't forget to add the new URL as the second argument.
You can find the documentation on these so called 'virtual pageviews' on this page (scroll to the bottom) on Google Developers.
Good luck!