Three hours later, I give up trying to figure this out on my own.
Basically, I've got a little smoke sprite as my particle type, and I have the null following the stroke and the emitter pick-whipped to the null. (Given the serrated nature of this shape, I may make a circular motion path with a light and have the emitter follow that.)
In any case, what I need is for the particles themselves to stay on the outside of the circle, and follow the direction that the emitter is traveling at any given time. Basically the smoke needs to be flung slightly outside the circular path that the emitter travels on.
I've tried animating rotation and wind and I'm just left with a big mess.