Try this:
<script>
$(document).ready(function(){
var tbody = $('#[% QuestionName() %]_div .inner_table > tbody');
$(tbody).append($(tbody).children().eq(0).clone());
})
</script>
If you're on an older version of Lighthouse Studio (and have an even number of rows), we may need to add on a bit more to make the alternating colors look good.