First you need to set up a custom domain as described here. This will allow you to match your display URL with your destination URL.
Google will approve a destination URL that is a sub-domain of your display URL. They just want to make sure the top-level domain of yourdomain.com match for both display and destination.
Example (acceptable) Destination URL: promo.yourdomain.com/product Display URL: yourdomain.com
An exception to this is if you're using a domain that hosts many different independent entities like blogspot.com or wordpress.com (blogspot.com as your display and myblog.blogspot.com as your destination would not be approved).