You could do what I do – use another plugin called WP Performance Booster. This lets you add the browser caching to your .htaccess. (You can also use it to set GZip compression and Vary: Accept-Encoding Header). Ideally you want to move things around so Leverage Browser Caching is the first thing in your .htaccess. Something like this:
# BEGIN WP Performance Score Booster Settings
## BEGIN Expires Caching (Leverage Browser Caching) ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg “access 2 week”
ExpiresByType image/jpeg “access 2 week”
ExpiresByType image/gif “access 2 week”
ExpiresByType image/png “access 2 week”
ExpiresByType text/css “access 2 week”
ExpiresByType application/pdf “access 2 week”
ExpiresByType text/x-javascript “access 2 week”
ExpiresByType application/x-shockwave-flash “access 2 week”
ExpiresByType image/x-icon “access 2 week”
ExpiresDefault “access 2 week”
</IfModule>
## END Expires Caching (Leverage Browser Caching) ##
# END WP Performance Score Booster Settings
Then after this you have the section line starting with the line # BEGIN WPSuperCache