Some years ago after spending a lot of time running into the frustrating issues expressed in this thread, I used some of the techniques others have suggested to bring my new glider from Baltimore to Indiana.

I then phoned several state license bureaus around the city and thought I had success when one said no problem...just bring the papers and come in. Rushed there and found the "foreign" registration agent on break. When she came back she refused to help me. Got the manager involved. She said it was going to take a long time and cost me a lot of money explaining I needed to get an engine emission test...for the trailer? After I tried to explain in a civil fashion that it was a trailer and had no engine, she fumbled through her pile of papers, handed them to me and said it was my problem. You go figure out what you need to do.

Finally I went to the office in a nearby small town where I found the license bureau folks and the local police officer friendly and helpful. Problem finally solved.