creating dynamically items in a plugins dialog

I'm developping a plugins displaying a dialog with a select menu. Depending on the selecting item in the list, I need to defined on the fly items (button, input, file input, etc). I know that one way is to create the items with "new CKEDITOR.dom.element('xxxxx');" appending it to the desired div element of the dialog, but the look, feel and behavior of the created item is not the same as the other items created through the contents dialog definiton elements, and the created item is not avalaible through the dialog.getContentElement function. Is there a way to create on the fly an item? Something like:
insertitemindialog('mydialog','{type:'text',id:'width_applet', label:'Width'}',afteritem).
Any help would be wonderful, I spent to whole day to figure out how to do that without success.
Thank you
Franck