Hah,
as it usually happens, I found the solution just after I submitted the question!
Turned out that the problem can be solved by using this custom HTML code below the form itself:
<script type=”text/javascript”>
//jQuery(document).ready(function() {
jQuery(window).on(‘load’, function() {
jQuery(‘#submit button’).click();
});
</script>
Note that using jQuery(document).ready()
function causes the code to be executed after the DOM is loaded, but before the form is fully initialised. If you want to have form validate the fields and prevent submission if something does not validate, you must use jQuery(window).on('load')
function.