This is just a hack but…
If you have de-minimized the javascript you should see around line #66 a long line of code that starts with “return [Q.href,….”. I replaced that line (all the way to the closing “]”) with the following to add the Facebook and Twitter buttons. All this does is add a couple of iframes for displaying the Facebook and Twitter buttons.
return [Q.href, '<span style="float: left; margin-right: 20px; display: block;"><a href="https://pinterest.com/pin/create/button/?url=' + document.URL + '&media=' + Q.href + '&description=' + Q.title + '" class="pin-it-button" count-layout="horizontal" target="_blank"><img border="0" src="//assets.pinterest.com/images/PinExt.png" title="Pin It" /></a></span><span>' + Q.title + '</span><iframe src="https://www.facebook.com/plugins/like.php?href=' + document.URL + '&layout=button_count&show_faces=false&width=10&action=like&colorscheme=light&height=21" scrolling="no" frameborder="0" style="display:inline; border:none; overflow:hidden; width:100%; height:21px;" allowTransparency="true"></iframe><iframe allowtransparency="true" frameborder="0" scrolling="no" src="https://platform.twitter.com/widgets/tweet_button.html?url=' + document.URL + '&via=xtapit&text=' + document.title + '" style="width:115px; height:21px;"></iframe><div style="clear:both;"></div>']
Adding the Google +1 button was trickier and requires a new php script in the plugin directory and changes to pinterest-lightbox.php