API: Show/Hide additional y axis

Hi,
I want to dynamically show/hide the additional y2 axis, as it may not be needed anymore after unloading data or before loading any data.
Currently, after I unloaded all data for the y2 axis, the y2 axis is still displayed, which is unnecessary and confusing.
The following jsfiddle illustrates the problem:
http://jsfiddle.net/nullundnix/fLgpu3br/4/
Is it already possible to achieve this or can it be achieved by changing parts of c3.js?
Any help would be greatly appreciated.