Oh my god, it's an image. It's just an image. I feel stupid again.
The image is named
letterbox_bottom_glass_overlay.tga
and can be found in the latest
skin art pack. When you are done with the repositioning of the levelmeter, grab the image, reduce the size of the image to fit your levelmeter (beginning from the center of the image; you have to keep image symmetric), resize the black space in the center of the image to fit the space between the two middle caps and, if necessary, move the alpha channel to make sure, that the gaps in the glass overly match match the gaps in the level meter fill image (the offest filter of Photoshop is very useful at this pint).
This is my final result:
