The City has outfitted our Rangers with Transit Connects.......equipped with spotlights. They used the traditional a-pillar mount. You can probably do the same thing.
I ran into a couple of them today, as I was on my way home. I was still wearing uniform pants, with a regular jacket covering my shirt. The girl driving the first vehicle said, "how did you get a new one, and unmarked?"
It didn't occur to her that I was driving my own car, not a city vehicle.