How to fill in the Primary Field with the value from an Option Set

Hi, I want to copy the value of a option set into the primary field within the same entity.  I found this blog that indicates that this is possible using a workflow but I am unable to make this work.  Here is the link to the blog: http://blogs.msdn.com/b/mvpawardprogram/archive/2012/02/27/microsoft-dynamics-crm-changing-the-primary-field-in-custom-entities.aspx

Can anyone assist with my request or point me to a good workflow tutorial.

Thanks

Dave