How to insert extra and hidden information for each element of document via LibreOffice API?

Hi everyone,

I am working with the Eclipse Papyrus team on a UML to odt generator. Besides one way generating, 
it should be able to handle bidirectional synchronization between these two "worlds".
For reaching this goal, I need to map each model element with its respective doc element. For 
example, a package name will be transformed to a section in a document or a comment in a paragraph. 
I am looking for a way to reference the UML element from the odt document, for example adding the 
ID of the UML element to an odt "paragraph".
In the users mailing list, Regina Henschel, suggested me to use bookmarks. It is a good idea, but, 
if is possible, I want to hide this information.

Does anyone have another suggestion?

Best regards,

Yupanqui