Probably doesn't require any previous experience with code. It's very simple.
- Download the Processing IDE from processing.org
- Download the LPL-processor code (on the left)
- Put your movie into lpl_processor/data/
- In the code, edit the moviePath, to match the name of your movie file.
- Optionally, change the blendMode. SCREEN is like traditional light painting, and LIGHTEST will allow for painting on top of a scene without over-exposing it.
- Run the script, and wait until it finishes.
- The composited frames will be in output/. Use the Processing > Tools > Movie Maker utility to create the final movie.
Find more light painting programs at lightpaintlive.com