Hi Vitaliy,
I think you are going to a wrong direction. The CKEditor is in javascript and if you need more information, you can go to the sample custom plugin of ckeditor, and actually there is a custom dropdown list plugin that may fit your requirement.What you need to do is to create a web service that allow the data needed to be retrieved by javascript. in the plugin.js file replace the following code:
// array of strings to choose from that'll be inserted into the editor
var strings = [];
strings.push(['@@FAQ::displayList()@@', 'FAQs', 'FAQs']);
strings.push(['@@Glossary::displayList()@@', 'Glossary', 'Glossary']);
strings.push(['@@CareerCourse::displayList()@@', 'Career Courses', 'Career Courses']);
strings.push(['@@CareerProfile::displayList()@@', 'Career Profiles', 'Career Profiles']);
with your web service datasource