@ProjectCustomizer.CompositeCategoryProvider.Registration(
    projectType="org-netbeans-modules-java-j2seproject")
public class BlaPanelProvider implements ProjectCustomizer.CompositeCategoryProvider {
    public @Override Category createCategory(Lookup context) {
        return ProjectCustomizer.Category.create(
                "Bla",
                "Bla",
                null,
                null);
    }
    public @Override JComponent createComponent(Category category, Lookup context) {
        return new BlaPanel();
    }
}