Is it possible to create an HTML canvas without a DOM element?

You can create a new canvas element with document.createElement:

var canvas = document.createElement('canvas');

and then get the context from it. Just make sure you set the width and height. You don’t have to add the canvas to the tree in order to make it work:

DEMO

But you definitely have to create that node. You could create a function for that though:

function createContext(width, height) {
    var canvas = document.createElement('canvas');
    canvas.width = width;
    canvas.height = height;
    return canvas.getContext("2d");
}

But that is where my competency ends… whether you can somehow transfer a context to another context or canvas, I don’t know…