The difficulty is due to how the open source packages of PHP, MySQL, and Apache are modified by Apple to integrate with the server installation.
The only sites I know that shed light on these issues are www.afp548,com and
http://osx.topicdesk.com/
There may be some stout-hearted individuals out there who have compiled and packaged installers for the items in question but mostly you will be on your own. If you chose to compile the software you will need to be aware of dependencies, file locations, and the possible need to modify LaunchDaemon plists and other config files.
You can pretty much install anything you want, but if the OS does not where the software location it will do no good. Also, if you do get your updated software installed be aware that you may not be able to use Server Admin to control the service any longer.
The websites and any discussion forum for Apache, PHP, and MySQL would also be another place to look as the odds are you are not the first to need an interim update.
You will also want to be sure you have installed all the current OS and security updates. Many times Apple will roll a patch for one or more open source programs into an update.
Good Luck