How to make the Webform submit button use an uploaded submit-image? I am building a D7 website and I want the following feature for the site admin, regarding the Webform module:

When the admin creates a webform, the admin uploads a submit-image and this image is used as the submit button for the webform. so if he uploads a "click-me.png" I want the path to this image to be used in the input[type=image] class="form-submit" src="/path to uploaded image" 

Is there a simple way to achieve this, or do I have to seperately hardcode the behaviour I want for each webform?

P.S. By default webform's submit button is of type "text" and not "image", but I easily managed to change this using this excellent solution.
The easiest way to do this would be to write your own module. The place to start looking would be here: http://drupalcontrib.org/api/drupal/contributions!webform!webform.api.php/function/hook_webform_component_info_alter/7