try this:
in admin/images.php find: show_additional_fields("image", array(), IMAGES_TABLE, $i);
Replace with: show_additional_fields("image", array("field1 => 0", "field2" => 0), IMAGES_TABLE, $i);
In admin/admin_functions.php find: show_radio_row($val[0], $field_name, ($value == "") ? 1 : $value);
Replace with: show_radio_row($val[0], $field_name, ($value === "") ? 1 : $value);
I dont know how these changes will affect other radio buttons (including none-custom)