Fields that are hidden from the front-end but editable in the back-end

I might be missing something obvious, but is there a way to include a field in a content template that will only show up in the back-end, be available using perch_content_custom, and will not show on the actual page the template is being used in?

For example, I have a portfolio page, and I want to be able to enter a tagline for the work. That tagline should only show up on the portfolio listing page using perch_content_custom, but not show up on the page.

Something like this

<perch:content id="tagline" type="textarea" label="Tagline" /> <!-- I want this to be editable through the backend, and available to use through perch_content_custom, but I don't want to show it on the page this template is created for -->
<p class="lead"><perch:content id="lead" type="textarea" label="Lead paragraph" /></p>
<img class="pic-web-site" src="<perch:content type="image" id="screenshot" label="Screenshot" />" alt="Image of web site" />
<h2>We discovered the problems</h2>
<perch:content id="problems" type="textarea" html="true" label="We discovered the problems" editor="redactor" />
<h2>We developed solutions</h2>
<perch:content id="solutions" type="textarea" html="true" label="We developed solutions" editor="redactor" />
<img class="pic-web-site" src="<perch:content type="image" id="screenshot-devices" label="Screenshot with devices" />" alt="Image of web site on different devices" />

-Rob