How to insert custom template into vB 4.1 template

[SiteTalkZone]

Hi,
I use vB4.1
I'd like customize my sidebar on memberinfo page. I would like add a custom template that I created before into somewhere in sidebar.
I create a new template called name 'mycustomtemplate'

<h2>{vb:raw testVarName}</h2>
<ul>
<li>Item 1</li>
<li>Item 2</li>
</ul>

And then, I create 2 new plugin, the first plugin use hook location: member_build_block_start, with following code:

$testVarName = 'testValue';
$templater = vB_Template::create('mycustomtemplate');
    $templater->register('testVarName', $testVarName);
$templater->render();

And the second plugin use hook localtion is cache_templates to register my custom template and it has following code:

$cache[] = 'mycustomtemplate'

Final, in MEMBERINFO template (reserved template of vB), I inserted following code into the position that I want to add my custom template.

{vb:raw mycustomtemplate}

However, when I visit my profile page, my custom template's content cannot be displayed.
I don't know what and where my problem is.

Please check and help me for this issue.

Thanks!