I've been researching this on an off for a couple of years and am finally in absolute need of it. I've seen lots of posts about people wanting this feature but no results.
I hate to alter the plugin but going through the code I've found onc place to make a simple override.
In /wp-content/plugins/w3-total-cache/lib/W3/mobile change line 21 from
return isset($_SERVER['HTTP_USER_AGENT']) && preg_match('~' . $group_compare_value . '~i', $_SERVER['HTTP_USER_AGENT']);
to
return isset($_SERVER['HTTP_USER_AGENT']) && preg_match('~' . $group_compare_value . '~i', $_SERVER['HTTP_USER_AGENT']) && ! isset( $_COOKIE['w3tc_mobile_override'] );
Then you just need to write the code to set and delete the cookie.
I haven't decided whether to take this approach, but it seems to be the most non-invasive way to handle this.
(also I tried to apply a filter to the cookie name but it kept causing a fatal error, could be this code is being called before that functionality is loaded)
