[Twenty-twelve]: Change header image on hover : Customize it!

Hello everyone.

Well I know how to replace the header image on hover with another one, using CSS.

But what I want is to add a specific field in the Customize menu of my theme, where I will select both the default header image, and the image that will replace it on hover, in order to be able to change both of them whenever I want. I have been struggling with the functions.php in order to do it, but couldn’t reach my target. As I mention on the title, I use the Twenty Twelve legendary theme ??

Could someone help me on this?

Thanks a lot!