If any of those contractors have deep pockets, I wonder if your stepson could find some young smart motivated attorney to file a civil RICO lawsuit...there might be a case to be made and a jury might just be willing to punish the employers of illegal aliens.
As much as I hate to get lawyers involved in anything, if our state/federal prosecutors and LEOs refuse to enforce existing laws, well then let 'er rip, sue the crooked employers for civil damages, class action or whatever.