Originally Posted by phxphlyer

I've tried three times, never been able to do it free of charge. I've never invoked the 20 minute delay rule, though. Something to try next time I guess.

I have, however, tried to switch immediately before the earlier flight is leaving, as smmrfld suggests, with no success. FYI I typically fly on the lowest of the low fare, and I fly a lot, but not enough to be a CP or A-lister.