how to add fo:block-container around title and subtitle on the titlepage

Hi folks,
  
 
  
I am trying to customize my_titlepage.xsl with the help of titlepage.templates.xml file which I will process with fo/titlepage.xsl.
  
 
  
What I need to define in this XML file is a <fo:block-container> around the <title> and <subtitle> elements, like so:
  
 
  
<fo:block-container>
  
 <title>
  
<subtitle>
  
</fo:block-container>
  
 
  
The problem is that I don't know how to define the block-container in XML, so that after processing this XML file with fo/titlepage.xsl, the title and subtitle will be inside the 
  
<fo:block-container> in the resulting my_titlepage.xsl.
  
 
  
Example from titlepage.templates.xml:
  
 
  
<t:titlepage-content
 t:side="recto"
             text-align="center">
 
  
  <!-- here I want the fo:block-container to start-->
    <title 
           t:named-template="component.title" 
           param:node="ancestor-or-self::article[1]" 
           font-size="&hsize5;" 
           font-weight="bold"
           keep-with-next="always" />

    <subtitle/>
 <!-- here I want the fo:block-container to end-->

        ...
  </t:titlepage-content>

  
 
  
Please,
 advise!!!
  
 
  
Thanks in advance!
  
Nancy