Is there a way to access an element's previous data inside of its `attrTween` tween function?

I want to update my donut chart's arcs using previous values of `startAngle`/`endAngle`, but it seems that the only way to access those angles is to cache them before applying a new data set. I know there is 3rd parameter in the tween function which is current value of the attribute, but in my case it's a raw string value of the SVG path's `d` attribute, something like `M53.86870,HURR-DURR...`. I'd like to use angles, calculated by `pie` layout and not to deal with the raw string.

[JSFiddle](http://jsfiddle.net/j0nj2h22/)