You need to modify:
\wp-filebase\classes\Item.php
adding a new role slugs:
if( ($for_tpl && !WPFB_Core::GetOpt('hide_inaccessible')) || in_array('administrator',$user->roles) || in_array('role-x',$user->roles) || in_array('role-y',$user->roles) || ($this->is_file && $this->CurUserIsOwner($user)) )