Thanks Jason, I believe I can use this in conjunction with a copy of the Add To Cart form post.
e.g. To get the item ID only after Add To Cart is used and not when page loads normally.
<?php
if (isset($_POST["eCart1_1_ATC"]) || isset($_POST["eCart1_1_ATC_x"])) {
$eCart1->MoveLast();
echo($eCart1->DisplayInfo("ID"));
$eCart1->MoveFirst();
} ?>
The above works as required to just get the ID. It's a start.
I think I will be able to make up a line of code to automatically display the shadowbox with the recommended items based on the item's "ID" and if an "ID" is present.
So far so good, thanks again.