base add-ons gem

module RapidFTR
  module AddOns
    def self.add_exporter(e)
      exporters << e
    end

    def self.exporters
      @exporters ||= []
    end

    ExportResult = Struct.new :data, :content_type, :file_ext

    def self.add_importer i # if you ever invent such a thing
  end
end

example exporter gem

require 'rapidftr/add_ons'

class CPIMSExportTask
  def export(children)
    # Code...
    RapidFTR::AddOns::ExportResult.new the_data, "application/pdf", "pdf"
  end
end

RapidFTR::AddOns.add_exporter CPIMSExportTask

Untested, so likely has mistakes.