This Whiteborad Friday blog post might be able to help. This clip helped us to cope and understand the post-panda environment. Combine the video with the data showing the falling rankings as proof that traditional SEO methods that get low quality links are no longer effective. Showing them other articles and videos on the changes since panda/penguin might also help to change their perspective.
They may be finding it hard to change methods and tactics because it has worked well for them in the past. Convincing them that their techniques are no longer viable can be quite difficult as they probably still believe that old methods are still the best. Perhaps if you compile a lot of articles or videos from top SEO experts, then perhaps they would come around an decide to change gears with their SEO campaign.
Hope this helps.