A seen on AC.com:
If an eUpgrade Nominee is not currently an Aeroplan Member, they can visit aeroplan.com to create an account. If your Nominee prefers to accumulate mileage with another frequent flyer program, they should add their Aeroplan Number to their reservation prior to the upgrade being requested, then
change their frequent flyer number upon check-in. This will not affect their upgrade request.
Source:
http://www.aircanada.com/en/aeroplan...des/share.html
Obviously, if AC allows and explains how eUpgrade nominees can use eUpgrades
and credit miles to another FFP, they certainly allow their own top tier members to do so. If they didn't, they would be breaking *A rules.
The agent was wrong. And according to that quote, it seems that you definitely can be waitlisted for an upgrade, change your FFP# during OLCI, and still be on the list!
This same thing happened to me a few months ago in CUN and AC/AE customer service has been unwilling to correct the agent's mistake. I'm currently pursuing the matter through *A.