Any chance you can pull up your reservation on continental.com and use their online check-in function? That's probably your best bet at getting added to the upgrade standby list remotely. Might be a longshot given the first segment on LH, but worth a try.

If you can't do it until you get to FRA, don't worry too much. BF upgrades within 24 hours of departure are generally not cleared until shortly before the flight closes.