[Replicant]

Open one of the articles on your site, enable sitebuilder, drag an ad module down below the article, edit the module, paste this code into an ad and save. You can select who sees it during the configuration of the module.
You will also want to disable comments for Articles to make the comment box disappear. You may have to hide the comments disabled message with CSS. I started a Discus account and tested the functionality, it works as expected. I am a bit confused as to why use the outside forum since the guest user has to signup for a discus account to post. Why not just have the user sign up to your forum instead?

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