Yes, I've done that! I took the Shimano Nexus dynamo hub off my old commuter and put it in my Downtube Mini. I used the original rim and spokes, which were a little bit too long, so I had to innovate a bit, and it's a most unusual looking wheel. I know someone's going to say it's a complete boondoggle, but it's holding up fine so far.

I'd try to explain, but a picture is worth a thousand words....