Before revision:  We suggest using the Buyer Trade Reduction (BTR) mechanism, a variant of McAfee's mechanism, that is feasible and simple (in particular, it is deterministic, prior-independent, and anonymous).
After revision:  We suggest using the Buyer Trade Reduction (BTR) mechanism, a variant of McAfee's mechanism, that is feasible and simple (in particular, deterministic, truthful, prior-independent, and anonymous).