It appears the shortcode uses the key order_count and not per_page. You can modify this on the View Order page, where the shortcode exists.
[woocommerce_view_order order_count="20"]
If you would want some kind of AJAX order loader you may have to make some significant changes.
A note order_count also accepts the parameter all which will get all orders. Perhaps that is a solution?
EDIT:
The shortcode uses the template file myaccount/my-orders.php. You could modify this to look through a certain amount of orders, seperate them into seperate divs and have it show the additional divs with each button press.
It is also in this template file where they actually get all the orders, so you could add a paged parameter to this and quite easily do the AJAX content load.