gistfile1.rb

def create
  respond_to do |format|
    if @my_model.save
      format.json do
        render :json => @my_model.to_json(:methods => [:owner_name]) #owner_name is a method that returns owner.display_name
      end
    end
    format html { ... }
  else
     format.json { errors... }
  end
end