Take a look at this page
CKEditor Developer Guid - StylesIf you add the StyleSheetParser plugin and set the stylesheet for the content, it should automatically parse the styles out of your stylesheet and add them to the dropdown list.
You could create a handler that you can somehow pass an argument to that will tell it which style sheet it needs to use for the editor and set that handler as the custom config file.
I am still researching to see if you can make a web part to add the styles after the page has loaded.