I have moving my joomla site from apache to nginx and also have handled to cope with all the mod_rewrites with relative ease. The only person that's been giving me fits, is perfect for a subfolder that holds my multisite wordpress install underneath joomla. The next resides within the '/blogs' directory of my joomla install. I have attempted a couple of attempts – even went it with the convert tool available, but no luck.

RewriteEngine On
RewriteBase /blogs/
RewriteRule ^index\\.php$ - [L]

RewriteRule ^([_0-9a-zA-Z-]+/)?files/(.+) wp-includes/ms-files.php?file=$2 [L]

RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule  ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule  ^([_0-9a-zA-Z-]+/)?(.*\\.php)$ $2 [L]
RewriteRule . index.php [L]