How do I get the Structured Data Testing Tool to ignore template elements?

Question

I’m using Web Components to build a site, and one of the biggest features is my use of the <template> element. Here’s an example:

<ul>
  <template>
    <li>
      <div class="c-ArticleTeaser" itemscope="" itemtype="http://schema.org/NewsArticle">
        <img class="c-ArticleTeaser__Img" src="{{ database__image }}" alt="" itemprop="image thumbnailUrl"/>
        <p class="c-ArticleTeaser__Hn">
          <a class="c-ArticleTeaser__Link" href="{{ database__url }}" itemprop="url mainEntityOfPage">
            <cite itemprop="headline">{{ database__title }}</cite>
          </a>
        </p>
        <p class="c-ArticleTeaser__Date">
          <time datetime="{{ database__datetime }}" itemprop="datePublished">{{ database__datetime_formatted }}</time>
        </p>
      </div>
    </li>
  </template>
</ul>

(A list containing a <template>, used for dynamically marking up article teaser items, each containing a headline, image, and timestamp.)

My front-end script clones the <template> content, fills in the missing data from a database, and then appends the newly-created <li> element to the end of the <ul>. The result is a <ul> with one <template> child followed by a bunch of <li> children.

When I run my markup through the Structured Data Testing Tool, it parses the “filled-in” articles correctly, but it also reads the dummy article in the <template> element. This throws a bunch of errors, such as:

Cannot understand the value {{ database__datetime }}

I can’t remove the template element from the DOM, in case it needs to be dynamically used again after page load.

Two questions:

1. How do I get the tool (and Google) to ignore <template> elements?
2. If I can’t, will these errors penalize my site?