gistfile1.rb

module Sunspot

  class ResqueSessionProxy < Sunspot::SessionProxy::AbstractSessionProxy

    attr_reader :original_session

    delegate :config, :delete_dirty?, :dirty?,
    :new_search, :search,
    :new_more_like_this, :more_like_this,
    :remove, :remove!,
    :remove_by_id, :remove_by_id!,
    :remove_all, :remove_all!,
    :batch, :commit, :commit_if_delete_dirty, :commit_if_dirty,
    :index!, :to => :session

    def initialize(session)
      @original_session = session
    end

    alias_method :session, :original_session

    def index(*objects)
      args = []
      objects.flatten.compact.each do |object|
        args << object.class.name << object.id
      end
      Resque.enqueue(Sunspot::IndexJob, *args) unless args.empty?
    end

  end

end

index_job.rb

module Sunspot

  class IndexJob

    @queue = :indexer

    def self.perform(*args)
      objects = []
      args.each_slice(2) do |(clazz, id)|
        object = clazz.constantize.find_by_id(id)
        # don't blow up if the object no longer exists in the db
        if object
          objects << object
        end
      end
      Sunspot.session.original_session.index(*objects)
    end

  end

end

1. put index_job.rb in app/jobs. Remove from that top level module
2. Register SessionProxy with Sunspot