from what i can gather they did this: style hair with hair-farm convert hair to splines. convert splines to very thin planes. use a vertex shader to move the verticies apart when the camera looks at them (creating alpha cards). apply alpha texture to planes.
You can use the Script Advanced Painter, it has a Hair Painter tool in it, which admittedly is pretty poor and all since it's a bunch of planes and alphas, but using a Spline and one of the countless Tools which allow you to 'plant' stuff on the models (per vertice or poly, etc...) you can get something workable.…