No module upload by the webinterface for Drupal 7

When I am going to a site Drupal admin interface on a Aegir server http://mydomain.tld//user/1#overlay=admin/modules/install , there is no possibility to add a module/theme by the webinterface instead of a normal Drupal installation on a non aegir server.
There is a message 'Installing modules and themes requires FTP access to your server. See the handbook for other installation methods.' But I don't want to install an FTP server, and let my site owners do the module/theme installation by the Drupal webinterface.

I found a solution for a regular Drupal 7 installation at http://drupal.org/documentation/install/modules-themes/modules-7#comment... , where they give the suggestion to change the owner of the directory /sites/default to www-data , but I am not sure about Aegir problems that can happen after changing the ownership from aegir user to www-data user.