Programming :: Adding Some Code To Like 50 PHP Files

I need to basically add some code to like 50 php files. It's basically a script that I want to add near the end of these 50 php files. I figured I could use sed to replace </body> with the code. However the code, is very long and has a bunch of newlines obviously. How would I be able to do this?
sed -e 's/<//body>/(all the text)/' *.php

Since it has newlines, I don't know how to paste it in cause it would take me to a '>' prompt without allowing me to complete the sed command. I want to insert this code.
Code:
<br><br>
<center>
<form action="test.php" method=post>
<textarea name="comments" cols=40 rows=6>