There is/was a German in California who bought a US registered DG-400 and later converted it to a German registration and flew it in the US. I am not sure if he is still in the US, but I thought that he had found a way to keep the German registration for at least a couple of years. Google Marko Rocznik und you will find him.

I think Marko is also an authorized LBA mechanic, capable of performing and signing off his own annual inspections, finding one in US in order to stay airworthy might be problematic.

GK