A sneaky idea crossed my mind reading this topic ... where informing ISPs doesn't work, perhaps embarrassing them might?
If a league table of reported spam sorted by the originating ISP were put on a web site showing the volume of spam reported by ISP - perhaps culled from Jeff's honeypot database? - and it is visible to the public, they may feel sufficiently ashamed or embarrassed to actually do something about it. It's years since I dabbled with SQL but I'm sure it should be relatively simple to do a count sorted by ISP

Jeff?