How can I get the insertpre plug enabled ?

I am trying to enable the following plugin. I added the following to my config.js but then after adding it I don't see any new buttons or icons for the <pre>.  I posted on stack overflow and the reply was "no you should not add it there, this is the file, when ckeditor builds"  If that's the case then where should I add it. Help would be much appreciated. 

CKEDITOR.editorConfig = function( config ) {
    // Define changes to default configuration here. For example:
    // config.language = 'fr';
    // config.uiColor = '#AADC6E';
    config.extraPlugins = 'insertpre';
};