Thank you for the good question.
It takes about a minute to find this nice solution
Code:
{literal}
<script type="text/javascript">
function printable_switch(){
var b = document.getElementsByTagName('body');
if (b){b[0].className = b[0].className == "printable" ? "" : "printable";}
}{/literal}
</script>
<a href="#" onclick="javascript: printable_switch();return false;">Printable/unprintable</a>