Wirelessly posted (BlackBerry8530/5.0.0.601 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
Redeem from JFK to DUB on EI. Very low fuel surcharges for EI TATL flights. From DUB to AGP, you can redeem more Avios on EI (but you will pay higher fuel surcharges on that leg), or buy a cash ticket on EI or a low-cost carrier.
Or you can fly to Brazil first, and pay no fuel surcharges at all (but use a lot more Avios).