Ah man, some bad news, sort of.

Just noticed that although it works, it's something that is going to need tweaking depending on camera angle, so you need to set your camera angle before setting up the stretch ratio.  The reason is that it's not actually distorting the camera, it's stretching the whole scene.

If I rotate the camera on that test, she is the normal aspect ratio from a side view!

Arrrgh!

Shame, although I suppose it could be fixed with scripting, something that causes the stretch to be independent of the camera view.  Basically, we're getting the Anamorphic bokeh, but it's effect is independent from the camera.  Shouldn't be a problem for stills but it's not going to work for animation if the camera rotates.

Still, the fact that we can render stills in Anamorphic format is fantastic, I'm going to be playing with this big-time!