I've tried on several occasions with flights USA (typically IAH)-YYC-YEG and was unable, even after trying to see if I could get Concierge to help, although I haven't tried in the past year. Prior to OSS it wasn't an issue - I'd simply collect my bag and head to the connections desk and get them to re-tag for stand-by. In USA at check-in was told that they couldn't place me on stand-by for a different station. At YYC was told that there wasn't enough time to get bags re-tagged prior to earlier flight. In each case I was trying to get a 2.5-3h connection down to approx. 1.5h.

I suppose it is possible that things have changed since I last tried to do this. I suppose it is also possible that this could have happened if I was trying to change a 8-hour connection to a 4-hour connection. My situation appears to be similar to OP, where the connection time/savings didn't justify the SDC fee - it just would have been nice to get on the earlier flight, so didn't want to previously comment on what might have been possible on longer connections.