document.getElementById('contact_form').action = "some_process_page_that_doesnt_exist.asp";

submit.Attributes.Add("OnClick","'submitConactForm();'"); 

function submitConactForm() {
    // Change the form action to the real submission page
    document.getElementById('contact_form').action = "process_form.asp";
    // Submit the form
    document.getElementById('contact_form').submit();
}