Many thanks for your promt response. I had feared as much, although it seems that if I cause the generation of a link such as

<a href="http://mystoreurl.co.uk/zc/index.php?main_page=product_info&amp;cPath=32_39&amp;products_id=154#back_in_sto ck_notification_form">notify me</a>

In the zen_check_stock function in functions_lookups.php (it's there that it discovers that there is a lack of stock) then it would generate a link into your process... or is it not that simple?