Follow these steps:
1. Download the Source Editing area plugin from http://ckeditor.com/addon/sourcearea
2. Put the sourcearea folder in the .zip file in qa-plugin/wysiwyg/ckeditor/plugins
3. Edit the qa-plugin/wysiwyg-editor/qa-wysiwyg-editor.php and add exactly this line:
" { name: 'source', items: [ 'Source' ] },",
Immediately below this line:
" { name: 'clipboard', items: [ 'Cut', 'Copy', 'Paste', 'PasteFromWord', '-', 'Undo', 'Redo' ] },",
4. In that file also add this line:
" extraPlugins: 'sourcearea',",
Immediately below this line:
" language: " . qa_js(qa_opt('site_language')) . ",",
And that's it. You should see something like this :)