I've had the luck to get into the first seats from CW a few times in the last 2 years. The first was due to a long planned change from 788 to 789 on YYC-LHR and a very full flight. Went to choose my seat and saw the seat map was showing seats available in both CW and the first cabin so picked 1A and stuck with it. Flight ended up being delayed by more than 7 hours so even got my €600 on top of a nice seat. Same thing happened next time I went LHR-YYC but some resistance to using the first cabin but CSM relented. Then back in July this year the seats weren't available but the CSM moved a couple of BA staff up there so I asked politely and 1A was mine once again. Same CW service just a much nicer seat/screen etc.

The CSM sometimes can't do it if staff numbers are low, so don't be cross to see it empty, but it has worked for me on three times out of four on the YYC route.