Broodlings spawned when selling a building are able to attack the destructable rocks.
Using a zergling building i constantly built and sold next to the rock allowing a constant flow of broodlings, my timing wasn't perfect but i managed to destroy the rock before the 6 minute game mark, i had 5 refinerys running at 10min 30 second gametime. Since the cost of doing this is only 30% of 95 minerals you can do this while making a small force or teching.