I've like this thread. this is something I've been looking at too since I realised my F707 was suffering with DLS (dark left side) slightly. Now I've got my '707 fixed, I don't use this manipulation now.
I used the 'gradient' feature on GIMP for Windows
to lighten the left hand side.
It can be used to counteract the darkening effect of vignetting too.
I'm sure the tool is available on Photoshop, you'll just
have to find it and adapt it similarly.
The first photo below is just black.
The second is the gradient applied only to the left hand side.
(Gradients >> Dialogues >> Opacity 50% >> Offset 50% >> Linear >> Lighten Only)
I've heavily enhanced the effect to show you what it looks like on black.
When you apply this gradient to your vignetted pitcures, go easy and start with
minimal values. If you overdo it, it looks really bad an you'll get hue changes.
The third is how the anti-vignetting gradient would look.
(Gradients >> Dialogues >> Opacity 50% >> Offset 50% >> Radial >> Lighten Only)
Get looking into your photoprogrammes and try it out.
I took me a few days to master it.
It is worthwhile.