Maybe you can get a modification like the One-Touch Spam Ban (called something like that) and when you come across a spam post, use that button to ban the user and delete all his posts. There is a time limit on that of the user having registered in the last 30 days, but you can change that. You can also give regular users the permission to use that mod so maybe a few trusted users can help out by using that mod when they see a spam post.