That's a tough one. I'm afraid that any effective solution may take a significant amount of effort and time. Essentially, you're talking about turning yourself into a community organizer. If you're serious, try approaching it from that angle. Look up effective strategies and tools for that type of effort.
I could be wrong. If you have a responsive police force, then maybe a few complaints would be enough to have them crack down, but the little history you've provided doesn't indicate that the responsible law enforcement agency is very proactive.
Fortunately, in my locale the drivers of modified cars are among the most courteous around cyclists. Actually, strike that: as a group, they are by far the most courteous, even better than LEOs. They can be, on occasion, a pain on the highways, but for whatever reason, around cyclists they pass safely and at reasonable speeds. In 30+ years of cycling in this area I've had one concerning encounter (a fairly close pass) with a driver of that type of car. The roads around here are fairly tightly policed, that probably has a lot to do with it.