Turning Nectar points into cash

Does anyone know the most efficient method of turning Nectar points into cash? The best I've been able to come up with so far is to spend the points on Argos vouchers (500pts for a £2.50 voucher), and to spend loads of them on something which has the 7 day no-quibble refund policy on it, and to then take it back for a refund. Would this work? And is there a simpler method or one that pays out more effectively?

Thanks