How to display user ad according to article submitter's username

[exuggs]

My pligg-powered site has several managers. I want to display different manager's advertisment on the article pages that are submitted by he/she. I build a .tpl file to contain every manager's advertisment code,such as Google AdSense. Then, I want to insert the following sentences into template.

{if file_exists($aticle_submitter_username.".tpl")}
{include file=$aticle_submitter_username.".tpl"}
{else}
{include file="the admin's ads file"}
{/if}

But I donnot know the default variable which means aticle submitter's username. Who can help me? Or tell me better or right way to solve the problem. Thanks!