Contour: label cumulative value

Hi,

Is it possible to label cumulative value in a contour?

I'm currently plotting a probability distribution by using gaussian_kde[1], but what I really care is the 0.68 percentage contour.

So instead of label the local value on a contour, is it possible to label a cumulative value?

Thanks!
Hong

[1]: http://docs.scipy.org/doc/scipy-0.14.0/reference/generated/scipy.stats.gaussian_kde.html#scipy.stats.gaussian_kde