Instead of hard coding use a javascript method
onclick
<form name="clickpay" id="clickpay" method="post"><input type="hidden" name="page" id="page"><input type="hidden" name="id"><a href="#" onclick="clickpay(clickpay);">Click Pay Link</a></form>
put a script to a src on your file system
<script src="http://yourwebserver/myscript.js"></script>
Encrypt / Obscure the javascript file:
http://www.stickysauce.com/misctools/js-encrypt/index.html
Anyway in the js file use something like
function clickpay(myForm){
myForm.page.value = "something";
myForm.ID.value = "123";
myForm.action = "http://mypagetosubmitto.php";
myForm.submit();
}
Anyway this is untested, but should work in theory except for perhaps some syntax bugs (been a while since I played javascript). Have them utilize the JS file from your server though.
-Geoff