This feature is not currently supported through a 'user-friendly' method; the present API allows easy retrieval of existing footnotes but not foot/endnote creation.
Of course it's possible to create a note through the low level OODoc::XPath methods (and a bit of knowledge of the OpenDocument Format), but it's not a smart way.
If such a feature is regarded as useful for a future release, please create a ticket in the issue tracker
(http://rt.cpan.org/Public/Dist/Display.html?Name=OpenOffice-OODoc),
describe the desired feature and select the 'wishlist' option in order to avoid confusion with a bug report.