title: Magento: Add column in sales order grid without join
body: <p>I need to add a custom column in the sales order adminhtml grid.
  Since I get the data for that grid from an external REST API by asking for data to a specific increment_id, I can't use the tutorials which are using a magento database to join the needed tables.</p>
  
  <p>Is there another way like:</p>
  
  <pre><code>function rendering_sales_order_row_before($rowdata)  {
      $columnContent = $restapi-&gt;callByIncrementId($rowdata['increment_id']);
      $this-&gt;addColumn("Custom Column", $columnContent);
  }
  </code></pre>
  
  <p>(This code should just illustrate my goal and I know that the solution will look completely different)</p>
  
  <p>Is it possible to achieve that in magento in an elegant way?</p>
  
  <p>EDIT: I'm using magento 1.9.2.1</p>