I totally agree. Used the BLK-STN and MAN-DUB many times with FR and when the online check-in was made available it was a god send! An extra hour in the sack!
You can print both boarding cards off when printing the outbound. I did it when on one of my GRO flights when I returned 5 days after departure. I printed the night before for both BLK-GRO and GRO-BLK.
Is there a limit to how far in advance you can print the return - say if you are away for a week or 2?