Our informed user zartc pointed this one out to us, as outlined in the Tomcat documentation here http://tomcat.apache.org/tomcat-5.5-doc/appdev/deployment.html chapter "Tomcat Context Descriptor" and here http://tomcat.apache.org/tomcat-5.5-doc/deployer-howto.html#A%20word%20on%20Contexts) the text says that TOMCAT 5.5.x supports deploying a custom context file from your project as long as it is contained inside of the META-INF directory and named "context.xml".

NOTE: It was previous thought that the file had to be named after your project (e.g. META-INF/myapp.xml) but this is infact not true and the file must be named context.xml.