<!-- TWITTER -->
<a expr:href='"http://bit.ly/?u=" + data:post.url + "&s=" + data:post.title + " (via @YOUR-TWITTER-USERNAME)"' target='_new' title='Tweet via bit.ly'>Tweet This</a>
somewhere within the DIV element
<div class='post-footer-line post-footer-line-1'>
Replace YOUR-TWITTER-USERNAME with your Twitter user name. See the original tip for more details.