EWR-FRA tomorrow (Thursday).

I was waitlisted for a GPU for ages, didn't clear. We are now inside the 24 hour mark, so the waitlist has gone to airport control. I can't check in online for some reason (perhaps because I am connecting to a LH flight?), which means that I can't get on the standby upgrade list. Have spoken to two separate agents, both told me there's nothing I can do, just have to wait till I check in at the airport, and then I will appear by magic on the upgrade list, and my position on it won't be affected.

Right now there is one seat left and no-one showing on the upgrade list.

Any suggestions, ideas? What can I do at this stage?

Thanks in advance for any help...