Future Request

If you have always one package per order, it should be quite easy to add a tracking URL.

First, create a custom order field via the menu Display->Custom fields and have it show only on the form of the backend. That will enable you to enter a tracking number in the back end for your orders.

Then, you can modify the file show of the view order of the front end via the menu Display->Views and add some code like this (supposing that the column name of your custom field is order_tracking_number ) :

<?php
if(!empty($this->element->order_tracking_number)){
echo ' Track your item: <a href="http://URL_OF_TRACKING_SERVICE'.$this->element->order_tracking_number.'">'.$this->element->order_tracking_number.'</a>';
}
?>

For example, for USPS the tracking URL is this: trkcnfrm1.smi.usps.com/PTSInternetWeb/In...rigTrackNum=00000000
So you would have the code:

<?php
if(!empty($this->element->order_tracking_number)){
echo ' Track your item: <a href=" trkcnfrm1.smi.usps.com/PTSInternetWeb/In...rigTrackNum='.$this- >element->order_tracking_number.'">'.$this->element->order_tracking_number.'</a>';
}
?>

After the order number seems like a good place. So after that code:
<?php if($this->invoice_type=='order'){
echo JText::_('HIKASHOP_ORDER');
}else{
echo JText::_(strtoupper($this->invoice_type));
}
echo ': '.@$this->element->order_number;
?>