What works for me is to fill in the panel line with liquid super glue only a little bit so that the original panel line is still visible. Then, I take a photo-etch saw blade and lightly saw a channel into the super glue using the original panel line as a guide. I gradually build up the panel line and saw the channel until the new panel line is built up. Don't bother with accelerator for the glue. I found that not using it provides a smoother surface for the saw blades. You can widen the new panel line using thicker saw blades or scribers.