There are so many services that work as mixers, that are not designed specifically to be mixers.
Make two accounts. Buy namecoin with one, send namecoin from one to the other through an external namecoin wallet. Do it with a delay (a few days) for best mixing. Then buy new BTC with the second account via the namecoin and send it as needed. If you trust them you can keep a small balance there as well. You pay less then a 2% fee overall.
Be sure to use reasonable mixing techniques, such as not using one large amount at once, and waiting time between transactions.