Turn off transactional fixtures for one spec with RSpec 2

I usually add a helper like this:

def without_transactional_fixtures(&block)
  self.use_transactional_fixtures = false

  before(:all) do
    DatabaseCleaner.strategy = :truncation
  end

  yield

  after(:all) do
    DatabaseCleaner.strategy = :transaction
  end
end

Which lets me turn off transactional fixtures for a specific block in the specs:

describe "doing my thing" do
  without_transactional_fixtures do
    it "does something without transaction fixtures" do
      ...
    end
  end
end