You could probably hard code this into the email-html file.
The HTML files for email are housed in the email folder (same directory level as admin, includes, cache, etc).
The file you need is probably the one called:
email_template_gv_mail.html
The following may work (no guarantee, but try).
Open the file to edit and find the following:
Code:
<!-- Content Section -->
<div class="content">
<div><!-- Dear --> $EMAIL_FIRST_NAME $EMAIL_LAST_NAME</div>
<div>$EMAIL_MESSAGE_HTML</div>
<div>$GV_WORTH $GV_AMOUNT </div>
<div>$GV_REDEEM<br />$GV_CODE_URL</div>
</div>
Either create a new DIV inside the above div nest, or, if you'd like it to stand out a bit, between two lines, say, then add this directly beneath the above code:
Code:
<hr>
<a href="http://www.yourwebsite.com/link">Go here for more information.</a>
<hr>
If you want to apply unique styles, then use <div>, and add your style to the embedded stylsheet on the page.