How to use another base_url instead of www?

I try to setup a structure like this:

http://we.areplayingwithdrupal.com/ (as main domain, eg: http://we.areplayingwithdrupal.com/admin/ etc)
http://children.areplayingwithdrupal.com/ (children is the name of the OG)

What I tried is:
- Setup subdomain for OG using the readme
- in Subdomain settings I disallowed www, we and static

In my settings.php I set the $base_path to http://we.areplayingwithdrupal.com

In .htaccess I added:

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

The subdomains are working as expected, the $base_url isn't. Whatever I try, all links still point to http://playingwithdrupal.com/LINK, so without the we. subdomain. Because of my htaccess rewrites the link resolves to the right location, but it's not really nice though.

If i remove we from the subdomain settings I only get 'Page not found' errors.

What could cause this? How can I change www to another subdomain as primary domain?