Yes of course there is. And this doesn't change the ticket to an LH ticket ... it remains a UA 016 ticket and will earn miles based on $$$ spent. It changes the flight number to the native flight number ... not the ticket stock!
Follow instructions here:
LH Electronic PlusPts Upgrades -How to use, will it clear?, issues w/flight credit,..
You call 1K and tell them you want to upgrade using +Ps and you need a conversion to the native LH flight numbers. Most agents know immediately what they need to do.
To do this efficiently, the booking class needs to be available on the native LH flight number - waiting too long to make the conversion can be problematic for that reason. There are ways around it, but it is a LOT more tedious. The simple flight number conversion is straightforward ... I do 10 a year.
Thank you so much! I finally got an agent at 1K Desk who knew exactly what to do, and got the upgrade request put through. I doubt it will clear, but I learned something!
The official FAQ does say you need to call when dealing w/ codeshare flights btw ...