Just curious if anyone else has had a similar experience (and ideally a solution!)...

On my recent flight back from YYZ to TLV via FRA, my final leg was on a Lufthansa codeshare. Realizing in advance that the eUpgrade process would not work on a codeshare, I called the AC Reservation Desk where the agent advised me that my only option was to try and upgrade in person at the Lufthansa desk. I asked if there was anything else I could do in advance to increase my chances, but was informed that this was the only option. Additionally, I called the Lufthansa reservation agent who gave me the same information. (I think I remember seeing similar advice on FT as well.)

In any event, I did try to get the upgrade in Frankfurt by speaking with a couple of Lufthansa agents, but they advised me that the only way I could upgrade would be if I had "a voucher" from AC so that they could recover the upgrade points/miles internally. The other option was paying the approx. 2000 euro difference in fare! (nope.) The agents seemed to be very confident of this voucher system, but I was left confused as I have never heard of such a process - aside from the old paper upgrade system. They were nice enough to give me an exit row, but it was somewhat tragic to see that the majority of the Business Class remained empty.

Is there some sort of "voucher system" that runs parallel to the eUpgrade system that anyone has experience with?

Thanks!