This should have what you're looking for:

http://www.aircanada.com/en/aeroplan/upgrades/eupgrades/share.html

"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."