It can be done, but it's not as arbitrary as a character count as the definition of what defines a "word" has some room for ambiguity. Try this:
<span class="[% QuestionName() %]_wordcount"></span>
<script>
$(document).ready(function(){
updateWordCount('[% QuestionName() %]');
})
$(document).on('keyup', '#[% QuestionName() %]', function(){
updateWordCount('[% QuestionName() %]');
})
function updateWordCount(questionName) {
var matches = SSI_GetValue(questionName).match(/\S+/g);
var count = matches ? matches.length : 0;
$('.' + questionName + '_wordcount').text(count);
}
</script>