Syncing the structure of two databases?

Dear list, I'm developing an intranet-based application using PHP and MySQL. We release new versions of our application regularly, and synchronizing the structure of the databases is beginning to be a headache. Do any tools exist that would let me sync the structure of two databases? Ideally, I'd like to include a "mysqldump --no-data" (or something analogous) file with each of our releases, and run a script on the client's server that would update the structure of their own local database from that file. We're cross-platform (windows, linux, and mac). And, all servers are behind their own firewalls. I'm aware of sqlyog (http://www.webyog.com/sqlyog/download.html), but I need something that can be written in php, and works without a "live" connection to the "master" database. Any clues? Thanks, Matt