It would be quite tricky. The only way to preserve full image quality would be to windowbox the 4:3- that is keep the same height of the frame but add black bars on the sides to fill the 16:9 framesize. Squashing the 4:3 to fill a 16:9 frame will lose resolution and quality- especially coming from a DV source like this.
I’d advise again this as it could detract from the piece as a whole visually. It’s always a good idea to settle on format before a shoot begins rather than switch mid-project.
Noah