You would need 2 functions to manage this ...
The current items.php uses a function to test should it show ...
PHP Code:
// disable only when entire cart is free shipping
if (zen_get_shipping_enabled($this->code)) {
$this->enabled = ((MODULE_SHIPPING_ITEM_STATUS == 'True') ? true : false);
}
You would want to add another function in there as well ...
That function would check how many items are in the cart for the Catalog side ... and on the Admin side would just return true so the module can work in the setup ...