Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
"Any idea how this could be done the more efficient with the least amount of points?"
Unfortunately, the most efficient will not be the cheapest. When you redeem BA Avios for TATL flights on AA, BA, or IB, there will be hefty cash surcharges assessed.
Consider BOS-DUB on EI, connecting to DUB-LON (any airport) on BA (you will have to call the BAEC Service Center to book this); then LON-TXL as a BAEC "Reward Flight Saver."
For the return from BCN, call BAEC and ask about availability for BCN-DUB-BOS on EI.