Someone like Cloudflare could provide feedback. They could insert a script into their "free" pages that would attempt to send DOS-like traffic to one of their own endpoints. If they come through, then embed a complaint about lack of SAV in the pages sent to that ISP. When enough customers call the ISP bitching that every page they go to complains, the ISP might eventually do something.

I'm not sure what CF's motivation for this would be, but I don't really understand their business model anyway, and they do lots of other nice things.