Alternately, you could use the Modify ePub plugin to replace the cover image page with one that has the svg wrapper bits and bobs set up for the size of image you are sending. It's likely a bit faster than manually editing your ebooks. The results be close to what @Karellen posted.
Spoiler:
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>A Guide to Papism</title>
<meta name="calibre:cover" content="true"/>
<style type="text/css" title="override_css">
@page {padding: 0pt; margin:0pt}
body { text-align: center; padding:0pt; margin: 0pt; }
</style>
</head>
<body>
<div>
<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="100%" height="100%" xmlns:xlink="http://www.w3.org/1999/xlink" preserveAspectRatio="none" viewBox="0 0 1000 1500"><image width="1000" height="1500" xlink:href="../Images/cover.jpeg"/></svg>
</div>
</body>
</html>