If you want to add parameters without modifying the form, you have to serialize the form, add your parameters and send it with AJAX:
var formData = $("#commentForm").serializeArray();
formData.push({name: "url", value: window.location.pathname});
formData.push({name: "time", value: new Date().getTime()});
$.post("api/comment", formData, function(data) {
// request has finished, check for errors
// and then for example redirect to another page
});
See .serializeArray()
and $.post()
documentation.