gistfile1.rb

# routes.rb
  match 'ads/:id/present/*path.:format', :to => 'ads#present'

# ads_controller.rb
  def present
    @ad = Ad.find(params[:id])
    path = "#{params[:path]}.#{params[:format]}"
    send_data(@ad.get_file(path), :filename => path, :disposition => 'inline')
  end

# ad.rb
  def get_file(path)
    tmp = Tempfile.new('unzip', :encoding => 'ascii-8bit')
    source = open(unit.path, 'rb').read # unit is the paperclip attribute
    begin
      tmp.write( source )
      zipfile = Zip::ZipFile.open(tmp)
      zipfile.each do |entry|
        if path == entry.name
          return zipfile.read(entry.name)
        end
      end
    end 
  ensure
    tmp.close
    tmp.unlink
  end