From http://stackoverflow.com/questions/8508514/how-to-run-jquery-directly-on-any-page-in-the-browser

add_jquery_to_page.js

var body = document.getElementsByTagName("body")[0];
var script = document.createElement('script');
script.type = "text/javascript";
script.src = "http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js";
body.appendChild(script);