I don't know about the anamorphic option in 3DE…
If it is a straight anamorphic and assuming that any lens aberrations have been removed (when processing the incoming plates), have you tried the default Camera Object's Pixel Aspect Ratio parameter?http://www.widescreen.org/aspect_ratios.shtml
As was mentioned before, you can render with the Mantra lens curvature property or set the camera Projection parameter to cylinder (panoramic) or polar (panoramic) to render non-ortho projections and is only supported by the raytrace or pbr Mantra render engines.
As far as rendering lens aberrations, you could use an Atmosphere fog Object in your scene that is assigned a fog shader to distort the field of view of the camera. This is only supported with raytracing and with larger deviations you will have to fire more rays as your coverage will vary in the scene.
The Atmosphere Object with the Fog Shader is applied last, after the displacement and surface shaders are run. This is why it isn't ideal to render lens aberration as it can lead to too much noise.
Another approach uses a physically based approach where you actually model a real glass lens out of geometry and parent this to the camera and fire rays through the lens. This means you will be relying on the index of refraction of your lens which is present on the Mantra Surface and the Glass materials. By changing the index of refraction on the shader, you can alter the amount of distortion.
Lots of fun but I don't know if this is something to rely on in production. I say this because you are spreading rays to cover a much larger area of the scene and you would need to fire more rays to reduce noise.