It is a common task on every WebSphere Portal setup.
Redirect the root “/” of the IBM HTTP Server to the context of WebSphere Portal ( /wps/portal)
Put the bellow lines on the httpd.conf and restart the IBM HTTP Server before the line of the WebSphere Plugin.
RewriteEngine on
RewriteCond %{HTTP_HOST} sample.com.br [NC]
RewriteCond %{REQUEST_URI} ^/$
Rewriterule ^(.*)$ http://portal.sample.com.br/wps/portal [L,R=301]