var script = document.createElement('script');
                script.src = 'http://canvas-text.googlecode.com/svn-history/r48/trunk/excanvas.js';
                script.type = 'text/javascript';

                var c = document.getElementById("myCanvas");
                context = c.getContext("2d");// getContext is undefined

<canvas id='myCanvas'></canvas>

var c = document.getElementById("myCanvas");
c= G_vmlCanvasManager.initElement(c);
context = c.getContext("2d");

document.getElementsByTagName('head')[0].appendChild(script);