I've been planning this for a few months now on and off, and even decided to try to fit this in as part of Bullet SoC work. I figured it would work quite well in furthering our goals of creating a Bullet Construction Toolkit, since visual tools are potentially more natural to use in the long run.
So, without further ado:
Presenting the Manipulators API Design Doc
Barring a need for significant re-architecturing, I'll start trying to implement this tomorrow, and hopefully there'll be some cool stuff to look at soon afterwards.