Take one monofilament (fishing line), place a ball of snot tape above and below the sensor cover glass in your camera, colour the monofilament with a blue sharpie, stretch the line and attach in camera. The effect reflects and scatters sharp highlights horizontally across the image. There you have it, anamorphic lens flares… or at least part of the effect.
The warning that comes with this post, is to be very cautious about anything in close proximity to the sensor cover glass and the back of a lens. The risk of scratching delicate coatings could be a costly repair bill, and don’t colour the filament inside the camera. Talk to the owner of the camera or the rental house first.
The anamorphic look is comprised of more than horizontal flares, the edges are soft, vertical stretch of out of focus images (bokeh), reduced depth of field, geometric distortion for wide angle lenses, oval flares, ghosting, breathing, poor close focus performance, poor field illumination, and chromatic aberrations.
The same flare effect can be achieved with a blue streak filter. The filter has parellel vertical blue lines. The effect of the filter is a very clean horizontal smear anywhere a highlight flares in the image. The single filament will only flare towards the middle of the lens and top to bottom. It seems more varied and random, and the shadow of the filament line can be seen under certain conditions.