WebDeveloperians, I need your help!

I've been using prettySociable on my site (can be downloaded here. I use the uncompressed version). I want to be able to change the tooltip (that shows up when you drag an image) to default to an image on my server, rather than to the page title. I think I've tracked down the code on line 265 of the jquery.prettySociable.js file, but I'm unsure how to change it:

Code:
// If no defined title, take the page title
					desc = ($('meta[name=Description]').attr('content')) ? $('meta[name=Description]').attr('content') : "";
					if(attributes.length==1) {
						attributes[1] = ['title',document.title];
						attributes[2] = ['excerpt',desc];
					}
Any help would be greatly appreciated.