Oops, just realized that you're using GtkComboBoxEntry.
There're some slight differences. The approach is the same, though.
Here's the corresponding examples using GtkComboBoxEntry instead of GtkComboBox:
http://www.kksou.com/php-gtk2/articles/setup-and-process-GtkComboBoxEntry---Part-2---using-data-view-model.phphttp://www.kksou.com/php-gtk2/articles/change-options-of-pulldown-menu-on-the-fly-using-GtkComboBoxEntry.phpRegards,
/kksou