Did you try his suggestions here, both for sitewide (the last one) or user education (the first three)? What were the results?
There is also the option to have some well-respected users (your community’s “influencers”) mention the expectation directly: “I don’t want to quote because…,” “just using this one quote to contextualize my thoughts,” etc.
You could also consider adding a “model post” topic, with exemplars, templates, or some fuzzier guides described as “best practice” for this or that type of topic or reply.
What type of guided modding are the users in the community most receptive to (e.g., converts most effectively to behavior change)?