[Zope] Zope security and packing the database

I have created a script based on zope_pack from the Zope book which allows a username and password to be specified when it is called. I wish to create a user specifically for this purpose that only has the ability to pack the ZODB. I've created a custom role and a user that has this role. Then I went to http://mydomain.com/Control_Panel/Database/main/manage_access and granted the backup role all available permissions. But the user can't login to http://mydomain.com/Control_Panel/Database/main/manage_workspace in order to pack the database. Obviously I'm missing something very fundamental here. Could anyone point me in the right direction please? Regards Cameron