Consider positioning yourself as a business owner/consultant vs. freelancer. You can create a section on your CV below your previous job or above it, depending on what is most current and is more impressive. Something like this:
"Your Name Consulting, 2004 - Present"
Offers design and development work to a range of clients (you can be descriptive and specify things like non-profits, small-medium size businesses or event cite specific industries they touched like education and health care clients). I specialize in deploying CMS platforms that extend to Magento, Wordpress, Joomla, and Drupal
If you want to go the extra distance, you can build yourself a very simple portfolio site to showcase some of your work. It will give employers added credibility to see what you've shipped and the type of skills you possess.