application.erb

stylesheet_link_tag(AssetCache::BASE_CSS, :cache => 'cached/base')

asset_cache.rb

class AssetCache
  include ActionView::Helpers::TagHelper
  include ActionView::Helpers::AssetTagHelper

  BASE_CSS = ['jquery-ui', 'formtastic', 'mogo']

  def warm
    stylesheet_link_tag(BASE_CSS, :cache => 'cached/base')
  end
end

assets.rake

namespace :assets do
  desc "Warm the asset caches"
  task :warm_caches => :environment do
    AssetCache.new.warm
  end
end

deploy.rb

before 'deploy:restart', 'warm_asset_caches'
task :warm_asset_caches, :roles => :app do
  run "cd #{current_path}; RAILS_ENV=#{RUBBER_ENV} rake assets:warm_caches"
end