Depends on how adventurous you are. If I had MY heart set on it...
mark the center of the bulb with a pin. heat up the plastic a bit if it won't poke - you're gonna use a hole saw anyways...
punch in a whole saw of the requisite lengths.
get the colour of plastic you need, but say 1/4 or 38ths thick anyway, and scribe out the circle. head to your band saw.
now buff the edges out - remember, you can't add material.
now set the circle into the cutout, and secure with some ca or krazy glue.
voila.
This gives you a 'tuner' button. you could spend alot of time shaping the disc to the contour of the lens, but it depends on the look you are going for.
Me, I like red.
