Me to had a same issue below is the apache2 config for the same kind of issue as describe below. Example folder is the rails application folder and "/en/blog" are the folder path in public folder of rails application in which i had a wordpress install so below configuration allow's apache to turn off passenger for a request made to "http:/example.com/en/blog" so this request is not process by passenger and this request is service as a normal php request so i was able to have a wordpress blog and a rails application running on same server.
# !!! Be sure to point DocumentRoot to 'public'!
DocumentRoot /var/www/example/public
#RailsEnv production
<Directory /var/www/example/public>
# This relaxes Apache security settings.
AllowOverride all
# MultiViews must be turned off.
Options -MultiViews
</Directory>
<Location /en/blog>
PassengerEnabled off
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /en/blog/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /en/blog/index.php [L]
</IfModule>
</Location>