Alas, no .. with Weather-Display or weewx-saratoga, the variables only exist in $tagname format.
But.. all the other plugins which use a [name]-defs.php to convert [name]tags.php entries into $tagname format that is used natively throughout the Saratoga template set. So your one-time conversion to $tagname from $WX['tag'] format would work if you switch to yet another weather software in the future.
For ease of switching weather software, I recommend not using the $WX[] tags as the names are unique with each weather software -- use the $tagname variables instead to add custom pages with markups. The ajax-dashboard and ajax-gizmo both have examples of using the $tagname format for common weather variables.