.htaccess - 301 to non-www to www version yet still allow subdomains

I've got a bit of a dillema. I'm trying to 301 redirect instances of:

http://example.com
http://example.com/
http://www.example.com

all to http://www.example.com/

I normally use this code:

RewriteCond %{HTTP_HOST} !^www.example\.com [NC]
RewriteRule ^(.*) http://www.example.com/$1 [QSA,R=301,L]

Code (markup):

Only problem is I use subdomains on this particular site so this code don't work. Any suggestions?

 

Try mine its a little different:

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

Code (markup):

 

Works great dude, thanks.