General: a Zone based on a Path

I was hoping someone has already written their own PathZone or PathZone3D. If not, it should probably be a new feature. Using something like a polyline or bezier curve and then applying a radius to it (or better yet sweep it with a shape). It would be especially helpful for defining 3D zones or when you have a *maze* you need your particles to crawl through.

If I want to attempt this on my own, I believe all I need to do is implement the Zone3D interface, which only has 3 methods:
contains(p:Vector3D):Boolean
getLocation():Vector3D
getVolumn():Number

Does anybody have any suggestions for implementing the polyline/curves? Are there any popular libraries that you recommend to build off of?

I think I could hack in polylines by myself, but by the time I got to curves I think my simple little class will have gotten quite messy.