Exclude directory from routing Options in CakePHP

Sometimes we would like to exclude a specific directory from any CakePHP rerouting. That directory may holds independent website or old website. Our .htaccess file should be like this 
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REQUEST_URI} ^/?(directory_to_exclude)/(.*)$ 
    RewriteRule ^.*$ – [L]

<IfModule mod_rewrite.c>
   RewriteEngine on
   RewriteRule    ^$ app/webroot/    [L]
   RewriteRule    (.*) app/webroot/$1 [L]

Example : RewriteCond %{REQUEST_URI} ^/?(oldsite)/(.*)$

Use (oldsite|test|new) for multiple directories.
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