...and the second entry Canonical Hostnames explains how you would achieve this.
Yes but I need a wildcard. I tried something like

RewriteCond %{HTTP_HOST}   !^www\.%1 [NC]
RewriteCond %{HTTP_HOST}   !^$
RewriteRule ^/?(.*)         http://www.%1/$1 [L,R,NE]
[download]

but not working. These rules are so hard :(