Indexes and custom sphinx_select searches

example.rb

class NewsEntry < AR::Base
  has_one :association

  define_index do
    index wadus

    has association.published_at, :as => :published_at
  end
end

class WadusController < AC
  def index
    # Here I'd like to use my defined filter attribute, but seems like it's 
    # using the regular 'published_at' attribute of NewsEntry. Is that possible?

    published_conditions = "*, if((published_at > NOW() OR published_at = 0), 0, 1) as published"

    conditions = {:sphinx_select => published_conditions,
                  :with => {:published => 1}}

    @collection = ThinkingSphinx.search(conditions)
  end
end