Help creating a plug-in that puts code into a template

[skedarisetty]

For addition of some "div" content into footer template, I have modified the template. the code for it looks something like this.

<vb:if condition="!empty($threadinfo[threadid])">
<!-- add two scripts -->
<div>
Some html code
</div>
<script type="text/javascript" language="JavaScript">
callme("variable1" ,{vb:raw threadinfo.threadid});
</script>
</vb:if>

I registered $threadinfo in the footer template and it is working fine. But I want to package it into a plug-in and put the same code into the template using that plug-in. So I created a template with above code chunk.

I created a product and a plug-in in it: I created the plug-in for the hook "parse_templates"
My Plugin code looks like this.
$tpl = vB_Template::create('mytemplate');
$template_hook['footer_test_hook'] = htmlentities($tpl->render());

and I put {vb:raw template_hook.footer_test_hook} in the footer template.

But nothing seems to render in the thread page. I would really appreciate it if some one guides me to the right way.