gistfile1.html

<!-- 
source: http://wordpress.stackexchange.com/a/53516/7577 
-->
<a id="buy" href="#">Buy this!</a>
<script>    
$('#buy').click(function(e) {
 e.preventDefault();
 addToCart(19);
 return false;
});
function addToCart(p_id) {
 $.get('/wp/?post_type=product&add-to-cart=' + p_id, function() {
 // call back
 });
}
</script>