Not sure if this is possible, but here's the breakdown of my situation.

Sunday: Friend (Elite) arrives in YYZ from Europe
Monday: Friend (Elite) and I (No Status) travel on the same flight (YYZ-YVR-LAS), but have different booking reference - as friend's booking is BCN-YYZ/YYZ-YVR-LAS, and mine is YYZ-YVR-LAS -- both bookings are Tango+ fares

Question:
Is it possible to use eUpgrades for our common flight YYZ-YVR-LAS for both of us? (Friend has enough eUpgrade credits for both of us to use)

If possible, can this be done online (I am one of his nominee)? Or must we do it at the airport at the check in counter?

If it has to be done at the airport, should we "check in" upon his arrival at YYZ on Sunday night (as I am picking him up)? Or wait till Monday morning to "check in" prior to departure?

Thanks.