title: Add property to ExpandoObject with the same name as a string
body: <p>Is there a way to add a property to an ExpandoObject with the same name as a string value?</p>
  
  <p>For example, if I have:</p>
  
  <pre><code>string propName = "ProductNumber";
  dynamic obj = new System.Dynamic.ExpandoObject();
  </code></pre>
  
  <p>I can create the property ProductNumber like:</p>
  
  <pre><code>obj.ProductNumber = 123;
  </code></pre>
  
  <p>But, can I create the property <code>obj.ProductNumber</code> based on the string <code>propName</code>?  So, if I don't know what the name of the property will be in advanced, I can create it based on this input. If this is not possible with ExpandoObject, any other areas of C# I should look into?</p>