Andre,
This would require custom code in a JS Code Extension. The Add Data Source option in the Data Layer Tab is to grab data that is already on defined on the page.
I am not sure if this will work for the Adwords verification. Meta data is really only functional if it is set on page load. Typically verification code will simply crawl the site/page to see check for the values. It won't load the files that are contained on the site.
I don't think the Adwords verification script will be able to pick up the values without loading the utag.js file as well, since Tealium will be injecting these values during page load.
With that said you can use something like the following in a JS Code Extension to append the meta tags to the of the page:
jQuery('head').append( '<meta name="description" content="this is new" />' );
This is assuming the jQuery library is loaded on the page.