Although it's not currently possible to use a dynamic link (as opposed to a hardcoded link) within a banner promotion while using the Magento "Query Merchandiser", it is possible to only specify the path in this URL field when using the "All Store Views" option. This gives some flexibility with the target link if used strategically.
If the path is the same but appears on two domains (ie: https://d1.com/path and https://d2.com/path), you can specify only /path in the URL field so it will stay on the current website domain (although the URL will open in a new tab/window).