The new Rollback menu item in the Change Package perspective rolls back all of the files attached to the committed Change Package.
A new workspace Change Package is created and can be committed. The revision attached to the Change Package is reverse merged out of the tip content. The reverse merge process itself is manual. You are prompted to run the merge using the Delta II tool. When the reverse merge is complete, the updated content is stored as part of the session. When committed to the current view, you get the desired effect.