Redirecting deleted/unot found blogs to a new system

hello wordpress wizards

I am upgrading from a subdomain based system using WPMU2.7 to folder based WP3.12 multisite system

i am redirecting

http://USER.domain.com/blogs/somethinhere/
to
http://domain.com/blog/USER/somethinhere/

the modrewrite that makes the job is

RewriteCond %{HTTP_HOST} ^(.*)\.domain\.com$ [NC] !-f
RewriteRule ^blogs/(.*)$ http://domain.com/blog/%1/$1 [R=301,L,NC]

however, i need to totally delete the old system (or rename it) for this code to work. as long as the old system is in place, wordpress current .htaccess overwrite the rule and simple send deleted old blogs to the main old blogs site….

how can i add the redirection above to work with the current .htaccess

RewriteEngine On
RewriteBase /blogs/

#uploaded files
RewriteRule ^(.*/)?files/$ index.php [L]
RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
RewriteRule ^(.*/)?files/(.*) wp-content/blogs.php?file=$2 [L]

# add a trailing slash to /wp-admin
RewriteCond %{REQUEST_URI} ^.*/wp-admin$
RewriteRule ^(.+)$ $1/ [R=301,L]

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

<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off
</Files>
</IfModule>

so, i could literally DELETE the blogs that i finished transfer and the server will point to the new system

thanks for any leads.