title: Add rows *on top of* column names Pandas Dataframe as header info?
body: <p>So I can export a DataFrame in a standard format, e.g.</p>
  
  <pre><code>A    B    C
  val  val  val
  val  val  val
  </code></pre>
  
  <p>But if I want the data to be reverse compatible with some older software I need to have 4 header rows, regardless of their content. It could be e.g.</p>
  
  <pre><code>nan  nan  nan
  nan  nan  nan
  nan  nan  nan
  nan  nan  nan
  A    B    C
  val  val  val
  val  val  val
  </code></pre>
  
  <p>Is there a simple internal way of accomplishing this? I guess one could export a CSV, then import it, and add the new lines, but that sounds like a hacky detour. Especially for many exported files.</p>