Assign additional users with Site Administrator priveleges

Cannot find how to assign additional users with 'Site Administator' access in the administration interface. In Vibe this has it's own heading, but is missing in Filr? This function is needed so the it can be administered externally not via the admin account, as it front ended via NAM so the admin account is not exposed. I don't want to have to VPN in and attach via 8443 to the Filr directly just to do administration.

Thanks,
Mark Currie