This might be late and maybe somebody's come up with the same answer but anyways...
On page 11 of this thread there are talks about how to generate a anisotropic direction map and I found a way.
First off, I've created some hair with the hair&fur plugin from 3dsmax. I set the renderer to VRAY and set the hairs to render as "geometry" instead of "buffer".
Here's the trick, you have to animate the "Cut length" in the "general parameters" of the hair&fur modifier so the hair grows over time. Once you've done that, you go in "render element" and add "VrayVelocity".
Basically, the anisotropic direction map has the green and red channel just like a velocity map. Since you're growing the hair, the velocity map created will end up being EXACTLY the aniso. direction map you need.
The only thing left is flipping the green channel and voilą. Here's an early test. I need to redo the hair patches and tweak the hair&fur but I think I'm on the right track!
*edit: forgot to say that this was done in UDK.