I have used a few redemptions to/from EZE (last one last Monday), but they're always difficult to find. Fortunately my travel dates for EZE are extremely flexible, so I always book according to redemption availability, and not the other way around.

You can try to find redemption to GRU/GIG and then a cheap ticket to EZE (there's even some AR flights to AEP now), but I reckon that defeats a bit the idea of a Club or First redemption.