Edit Invoice Template

I want to add at the invoice of the orders two extra fields.

1)Add Customer Group of the customer to the invoice

2)Add the date that the customer has made registration the site

I went to admin/view/template/sale/order_invoice.tpl and tried to edit the file.

I managed to add logo and some text e.t.c but i can not figure out how to add
the Customer Group of the customer and the date that the customer has registered to the site.

i tried <?php echo $order['customer_group_id']; ?>

<?php echo $order['text_customer_group']; ?>

But nothing worked. Anyone has any idea how to accomplice these modifications?

Or any extention paid or not that can add this two features in the invoice?

You cant just add it in the .tpl file and expect it to work......you would also need to add relevant code into the controller