 <p>You can do this with <a href="http://drupal.org/project/content_taxonomy" rel="nofollow noreferrer">Content Taxonomy</a>'s Content Taxonomy Options module. Add a new Content Taxonomy field, and use the Select widget. In the field settings, under the <em>Advanced settings for hierarchical vocabularies</em> field group, select the Parent Term you want to use for that field.</p>