Add a canvas element as overlay for freehand drawing

Hello, 

I' m working on a viewer for construction designs. I wan't to draw freehand on a fullpage overlay with fabric. js. I need a canvas as overlay for drawing. When I try this code I have 2 canvas elements, one on the viewer an one smaller (blank) for drawing (see picture). Is there any other solution?

Markus

![freehanddrawing](https://f.cloud.github.com/assets/4731267/1233861/b8245064-2947-11e3-89bc-1bf31940551e.jpg)

![code](https://f.cloud.github.com/assets/4731267/1233887/0b41763a-294a-11e3-95c4-1243dbd43484.jpg)