How to exit (or silent) remainder of parent html which includes me?
===

I have hundreds of already-existing HTML files, all using SSI to conditionally include a specific PHP short script. If the condition is true, the script is included after HTML and HEAD tags already sent to the browser. All of this is given.

What I really want to do in this PHP script is to prevent the whole page from being further processed. My best choice is to be able to redirect to some other page. My second best choice is to ouptut some specific HTML code from the script, INSTEAD of the HTML code that would be output after returning from the script.

Now here is my problem:

1. I cannot use PHP header redirecion, because some things have already been sent to the browser.
2. I don't WANT to use client-side redirection, because I want the user to be totally unaware of it.
3. If I echo my own HTML from the script and then exit() or die(), it returns to the parent HTML and outputs the remainder of the page.

What I really look for is a function like dont_output_anymore() or exit_html_parent() or similar... Help?