helper.rb

def grouped_options_from_enum(model, enum, label)
  grouped_options = [].tap do |opts|
    model.send(enum.to_s.pluralize).keys.each do |enum_value|
      opts << [enum_value.humanize, model.send(enum_value).collect {|obj| [obj.send(label), obj.id]}]
    end
  end

  grouped_options
end

This probably isn't even safe, but I needed this abstracted because it's used in several places for different models and enums.