I think I've discovered that the target of the prefetch is irrelevant, and that what matters is that the store-to-load forwarding does not try to execute in the same cycle. For Sandy Bridge, I'm finding that I can get slightly better performance with a dummy load of an unrelated volatile variable:

  volatile unsigned dummy = 0;
  void loop_dummy_read() {
    IACA_START;
    unsigned j;
    unsigned dummy_read;
    for (j = 0; j < N; ++j) {
      dummy_read = dummy;
      counter += j;
    }
    IACA_END;
  }