If you want to add that HTML to the overlay-style cart that appears "inside" your own page, you can do that using cart customization code. Just add the following to your View Cart code on every page, just before the "// -->" line in the standard code you obtain from Seller Admin.
function EJEJC_config() {
EJEJC_POSTCALL=true;
}
function EJEJC_shown() {
jQuery("#tdPmnt").attr("innerHTML","<script type=\"text/javascript\"><img id=\"cy_image\" width=1 height=1 border=0 alt=\"\"><script src=\"WebEvent.js\" type=\"text/javascript\"></script><script type=\"text/javascript\">cy.UserId=\"[%payer_email%]\";cy.Product=\"[%item_name%]\";cy.FunnelLevel=\"3\";cy_getImageSrc();</script>");
}
The line from jQuery("#tdPmnt").attr("innerHTML"," all the way to cy_getImageSrc();</script>"); would need to be all on one long line (despite the soft-wrapping you see here). If you're already using other cart customization code, just add that line under "function EJEJC_shown() {", before the closing "}".
We cannot vouch that this would even work for the purpose you describe, and there is no way for us to obtain the buyer's email at this point, since that is only provided by the buyer during checkout and then passed back to our system by the payment processor after payment is completed. Also, [%item_name%] and [%payer_email%] can only work on the thank-you pages/emails generated by our system, unless you are using those for purposes unrelated to our system.