Blendr filler for Bontrager stems

I'm a big fan of the [Bontrager Blendr system](https://www.trekbikes.com/us/en_US/bontrager_blendr_how_to/) for mounting things to the compatible stems. You can mount a Garmin and a headlight onto your bike without a single rubber band or screw-on mount wrapped around your handlebars, resulting in a really, really clean look to the front end of the bike. That said, sometimes you don't want or need to mount accessories to your Blendr-compatible stem, so you wind up with a blank space and a hole b