Conditional config WP_HOME/WP_SITEURL does not update bloginfo(‘template_url’)?

Found the solution… the problem was due to placement of the conditional statement in the wp-config.php file.

It needed to be inserted before the require_once(ABSPATH . 'wp-settings.php'); line near the bottom of the default config file, otherwise the constants are already defined and cannot be redefined.

So final section of the wp-config.php file now looks like this:

...

/** Add xip.io support for mobile theme testing **/
require_once('b5f-browsers.php');
if( b5f_browser_check('mobile')) {
    define('WP_HOME','http://mysite.dev.'.$_SERVER['SERVER_ADDR'].'.xip.io');
    define('WP_SITEURL','http://mysite.dev.'.$_SERVER['SERVER_ADDR'].'.xip.io');
}

/* That's all, stop editing! Happy blogging. */

/** Absolute path to the WordPress directory. */
if ( !defined('ABSPATH') )
define('ABSPATH', dirname(__FILE__) . "https://wordpress.stackexchange.com/");

/** Sets up WordPress vars and included files. */
require_once(ABSPATH . 'wp-settings.php');