RewriteEngine On
RewriteOptions MaxRedirects=3

RewriteCond %{REQUEST_URI} !^/$
RewriteCond %{DOCUMENT_ROOT}/root%{REQUEST_URI} -f [OR]
RewriteCond %{DOCUMENT_ROOT}/root%{REQUEST_URI} -d
RewriteCond %{REQUEST_URI} !^/some_dir
RewriteRule !^/?root/ /root%{REQUEST_URI} [PT,L]

RewriteCond %{REQUEST_URI} !^/?script/testapp_fastcgi.pl
RewriteRule !^/?root/ script/testapp_fastcgi.pl%{REQUEST_URI} [L]