[Plugin: Simple Nivo Slider] Add a second caption custom field

I am using the Simple Nivo Slider particularly for the custom field caption feature. I am trying to figure out how to add a second custom field, kind of a description or sub-caption.

I found this code in simple-nivo-slider.php:
$caption = get_post_meta(get_the_id(), 'simple_nivo_caption', true);

I am thinking I can define the other custom field like this:
$caption2 = get_post_meta(get_the_id(), 'simple_nivo_sub_caption', true);

Assuming this is the right way to go about it I am having trouble finding where the $caption is echoed to create the caption itelf. The code directly below this in the file appears to use it as the title for the image and not for the caption itself. <?php echo $linkhead ?><img src="<?php echo $imgsrc ?>" alt="" title="<?php echo $caption ?>" /><?php echo $linktail."\n" ?>

Any help anyone could offer is greatly appreciated.

Thanks.

https://www.ads-software.com/extend/plugins/simple-nivo-slider/