Syncing navigation across multiple platforms

I’m going to be building a large site in concrete5 with its blog in WordPress. The main site will be http://www.example.com with the blog at http://www.example.com/blog. One of the things they will share is a global navigation bar at the top of each page.

However, there are several small microsites as subdomains (handled by different CMSs) that will also need access to said navigation. I won’t be re-coding these microsites except to provide them with access to all show the same nav links.

I’m planning to write a script that will generate the HTML for this nav and write it an HTML file. I could set up a simple CRON job that would run said script every so often and update the HTML file. This way, I could tell these microsites to do a PHP include() and everyone would show the same nav.

I want to think this sounds sensible, but I have sinking feeling I’d be bringing a knife to a gun fight.