(case c="(qd)whichfile(/qd)")
    <file1><insertfile>....
    <file2...
  (/case)

or 

   <case c="<qd>whichfile</qd>">
     <file1>[insertfile]...
     <file2>[ins...
  </case>

and for the nitpickers just a simple

  <insertfile><qd>whichfile</qd>.xml</insertfile>