multisite shared calendar

So we run our school district main page as well as a separate site for each of our schools with the multi site feature of Drupal. There is a main District site and then 9 more sites, one for each school with a separate database for each school. Each of these individual sites maintains their own calendar using the calendar and date modules. I was recently asked if we could have the calendar on the main district site fed by all of the individual site calendars. Using the feeds module has gotten me close but not quiet there.