Indeed - just ran into that issue a bit with creating light graffiti in motion on a standard DSLR and had to resort to post-processing, though we figured it out eventually. Still def prefer a more direct/analog route where possible for sure. For stillframes shouldn't be much of a problem.
light graffiti? got any pics?
Here's a video we did with a dancer named David Elsewhere using the technique I mentioned earlier, esp. in the second nighttime half:
Wouldn't mind getting another crack at something like this as there are lots of elements I would improve personally but overall happy with the effect. (:
ah really nice technique! i would ask you how you did it but... a magician should never reveal their tricks.