I just did this in Frankfurt Airport. It is very easy there, even though FRA is kind of a confusing airport at times. For carry on bags, just past security line/passport control there is a custom office (get the paperwork from LV stamped there) and Global Blue right next to it. They can give you the cash (in Euros) or credit card. I did the cash. I would allow extra time but in my case I didnt need it. Custom asked if I had the items on me, which I did, but they did not ask to see them.
Also LV in Germany asked if I wanted to pay in Euros or USD. I chose Euros as I dont pay a fee on my credit card.