Dave,
Have you found a solution to this yet? You can pass along information from page to page using what I call URL Tokens. The php page is then programmed to look for these tokens and then continue to pass them on to the next page and so on.
Example page url: somedomain.com/page.php?token=value
The very first variable key, or token, is always proceeded by a question mark. If there are other tokens in the url, then they are proceeded by an ampersand. (&)
The key in the example is called token, but can be any alphanumeric.
If the page.php file doesn't have any coding to look for "token" token, then it just ignores it. But if it is programmed, then it may look a lot like this:
<?php if (!empty($_GET['token'])) {$token = $_GET['token']} ?>
So then later on in the page.php code, when you put in a link like <a href="page2.php"> you could pass on the token from the variable called $token in our example. Here is what it might look like:
<a href="page2.php<?php echo "?token=$token"; ?>">