In PL5 you can try this
shown here in mask view
- set a really big Control Point and reverse it
- pull Chroma / Luma slider all to the left
(turns the control point into a circular radiant filter) - adjust Opacity, Exposure, Control Point size to taste
resulting in a very soft vignette (closer to CEP4 / DLC than FP’s Creative Vignetting PlugIn).
