I see that most Zlins that are up for sale are registered in former Eastern-block countries. Whilst it may be legal for you to keep them under the original registration, it might not be very practical unless, of course, you speak fluent Polish or Hungarian.
A transfer to the German register is probably the best option for you, I wouldn't even consider setting up a trust in order to get an N registration for such a small plane.
Ciao,
Dg800