I'm going through a similar situation where I'm flying AC112 tomorrow and got a notification of a 2h delay. I called the concierge and asked to be put on an earlier flight that showed J space based on the AC app, but was told they would have to check to see if anyone else was on the upgrade list (the AC app shows nobody on the list) and they would have to do it via manual manipulation. I asked why in the past when upgraded to J and changing flights due to a posted delay was never an issue and was told it's different when using e-upgrades (I don't believe it).
I'm now waiting for an email confirmation but might call back in later so see if the concierge was able to do what I feel they should have been able to do easily.