I did a little google searching.
With NURBS alone, the mathematics seems to make this very difficult and uncertain. (grasshopper posts)

Manipulation with subdivision seems possible, but the math formidable, for example:
http://www.sciencedirect.com/science/article/pii/S0377042705004826

I came across "wavelet interpolation," "snake rigging", Maya Lock Length, tractrix, and clothoid extension (no free download),
and cannot read Chinese...:-)

Currently downloading LyX and browsing I Eat Bugs For Breakfast:
http://www.lyx.org/Download ........Are there any favorable or unfavorable comments?
Browsing https://ieatbugsforbreakfast.wordpress.com/2016/11/

- Brian