Needed the same functionality in the “My Latest Photos” widget so tracked this down.
For those that need a hack for the time being, you can change line 95 in the simply-instagram-functions.php file to
$output = '<a href="' . $data['data'][$i]['link'] . '"
target="_blank" title="' .
htmlspecialchars( $data['data'][$i]['caption']['text'], ENT_QUOTES ). '">';
The instagram link URL is being stored in $data[‘data’][$i][‘link], from there you can make the output whatever you would like.