submetendo um form para o google spreadsheet sem redirect

pagina.html

<script type="text/javascript">            
    var submitted = false;
    function submit(){
        if(submitted) {
            alert('Obrigado por cadastrar seu e-mail!'); 
            document.getElementById('entry_0').value = '';
        }
</script>
<iframe name="hidden_iframe" id="hidden_iframe" style="display: none;" onload="submit();"></iframe>

<form action="SPREADSHEET_URL" method="POST" id="ss-form" onsubmit="submitted=true;" target="hidden_iframe">
<!-- RESTO DO FORM -->