And if you want to stick with the GET method, you can use the fact that browsers won't send disabled fields. So tie into the onsubmit handler and disable any empty hidden fields like the following:
@using (Html.BeginForm("Calculate", "Home", FormMethod.Get, new {onsubmit="DisableNullFields();"}))
{
@Html.TextBoxFor(x => x.Test)
<input type="text" name="TestField" />
<input type="hidden" name="hidden" value="" />
<input type="submit" value="Push"/>
}
<script>
function DisableNullFields() {
$('input[type=hidden]').each(function(i) {
var $input = $(this);
if ($input.val() == '')
$input.attr('disabled', 'disabled');
});
}
</script>