I knew to copy the generic them, but I was doing everything except making the DocumentPaneTabPanelHidden. Came to me after dreaming it over last night:
<xcad:DocumentPaneTabPanel x:Name="HeaderPanel" Grid.Column="0" IsItemsHost="true" Margin="2,2,2,0" Grid.Row="0" KeyboardNavigation.TabIndex="1" Visibility="Hidden"/>