This point was raised in Converting doserLESS Rocky to DOSER... yeah that's right! The most cost effective solution may be a trade arranged on Coffeegeek's Buy, Sell, & Trade forum. Or live with a few clumps, assuming it doesn't ruin the quality of your espresso.
OTOH, a coupla cups of yoghurt at the local organic grocery and a pin in a stick is probably the easiest, fastest, and cheapest route, if the clumps are the onliest issue.