Make your client template as this :
.ClientTemplate("<a class='MyClass' myAttrib='<#= Value1 #>') title='Modify'>...</a>")
Then write the following scripts at top of your page:
<script>
$('a.MyClass').live('click',function(){
var myVal = $(this).attr('myAttrib');
OnModifyDescription(myVal);
});
</script>
Check this for jquery live
function : http://api.jquery.com/live/