I don't know for sure if this would work but I think it might.
Why not use the Better Business Bureau to complain about how a fleet owner is treating you? Even though the fleet owner is leased to the carrier they are still an independent business. By notifying the BBB using their proper channels they could become a clearing house for your complaints, as well as other people you run across that have worked for the same fleet owners. If it was suggested in a post on this site to include the BBB when researching a carrier or owner, the information you are trying to share would be there. In addition, the BBB will send the perpetrator a letter asking them to explain the problem or resolve it within 30 days. If it isn't resolved they give them a rating of "unsatisfactory". I have dealt with them for years and have gotten positive results in doing so. Just a thought.