This is not something built into the Spark Pay online store, however it can be accomplished very easily with some simple jQuery.
This is an example:
<div class="ac-expand">
<div class="ac-expand-link">
<a href="#">Show</a>
</div>
<div class="ac-expand-content" style="display:none;">
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Etiam iaculis dignissim nulla et dictum.
Donec dignissim ligula leo, vitae commodo purus.
Vivamus elementum mi vel nibh dapibus vulputate.
</div>
</div>
<div class="ac-expand">
<div class="ac-expand-link">
<a href="#">Show</a>
</div>
<div class="ac-expand-content" style="display:none;">
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Etiam iaculis dignissim nulla et dictum.
Donec dignissim ligula leo, vitae commodo purus.
Vivamus elementum mi vel nibh dapibus vulputate.
</div>
</div>
<!-- This one will be shown by default. Notice the Text of the link says "Hide" instead of "Show" -->
<div class="ac-expand">
<div class="ac-expand-link">
<a href="#">Hide</a>
</div>
<div class="ac-expand-content">
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Etiam iaculis dignissim nulla et dictum.
Donec dignissim ligula leo, vitae commodo purus.
Vivamus elementum mi vel nibh dapibus vulputate.
</div>
</div>
<script>
//make sure this matches the default text you put in the link above
var sShow = "Show",
sHide = "Hide";
$(function(){
$(".ac-expand").each(function(){
var $link = $(this).find(".ac-expand-link a"),
$content = $(this).find(".ac-expand-content");
$link.click(function(e){
$content.fadeToggle();
$link.text( $link.text() == sShow ? sHide : sShow );
e.preventDefault();
});
});
});
</script>