Right! Result! I could not do it online, so I called BA to have it done. After a bit of time on hold, I was able to choose the seats free. I may or may not be changing it back to BAEC depending on when I get my QF LTG - if I manage to do it before or extremely close by then, then I'll change to BAEC. If not, I'll leave it with QF. The question would of course be whether QF would manage to credit my Upgraviosed flights correctly at WT+ - I may well have to retro-claim.