Jose,

  I am not aware of an easy way to do what you are asking.  You could fake this behavior by creating different portals (each having its own domain or subdomain) and then using the ability to have pages link to a URL.  However this would require managing the pages in multiple sites which could get a little messy.  The other alternative would be to write some custom Advanced URL rules to handle redirection to the appropriate domain based on the page.  That also could get a little messy (although still better than maintaining multiple sites).