To resolve this you should use javascript. With javascript it'll be easy for your affiliates to implement and it's easy to create.
The only thing you will have to do is to create a javascript which renders a form with a submit button and adds it to the html documents DOM. This submit button should take all 4 values from this form and send the data to your server (using get or post).
A really easy example:
Implementing:
1) Your affiliate should reference your script from your server:
<script type="text/javascript" src="http://yourserver.com/yourscript.js"></script>
2) And also add an empty div which you will add your form to:
<div id="formForYourWebsite"></div>
Your script:
function createMyForm(){
var s = '';
s += '<form action="http://yourserver.com/script.aspx" method="get">';
s += '</form>';
var container = document.getElementById('formForYourWebsite');
container.innerHTML = s;
}
function addLoadEvent(func)
{
var oldonload = window.onload;
if (typeof window.onload != 'function'){
window.onload = func;
} else {
window.onload = function(){
oldonload();
func();
}
}
}
addLoadEvent(createMyForm);