Be sure to read the developer docs and include the correct ShareThis widget JS file with your publisher Id prior to this code [ something like http://w.sharethis.com/widget/?tabs=web%2Cpost%2Cemail&charset=utf-8&style=default&publisher=(pub-id) ]
What I've done is loop through any cases where the sharethis class is present. Inside the link include all the necessary information in data-* attributes that we pull out using jQuery.
Example customized ShareThis Link
<a class="sharethis" data-id="(uniqueid)" data-title="The Title of This Post" id="sharethis-(uniqueid)">Share</a>