addPath is currently defined on the Path2D object. [1] Is there a reason why it's not defined on CanvasPathMethods instead? That way this method is available on the 2d contest so you can append a path to the current graphics state.
This would also negate the need for setCurrentPath. 1: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-path-addpath
