[bes]

примерно так

(function () {
	var script = document.createElement('script');
	script.src='jquery-1.8.3.min.js';
	document.head.appendChild(script);
})();
window.onload = function () {
	alert($('body').html());
}

про document.head
https://developer.mozilla.org/en-US/...Fdocument.head