I have tried quite a few methodes to deal with negative inversion (including ColorPerfect). Finally I have settled on a method that gives consistent result and that is not to time consuming. I give you my 10 steps to try and see if it works for some of you as well, it maybe look complicated but when you learn the workflow it just take a few minutes.
1. Start with a 16-bit linear scan - Silverfast of Vuescan doesn't mather, Epson scan is not perfectly linear but work ok. The scan should contain a bit of unexposed area.
2. Start PS and open the file - with color scans I use to work in Adobe RGB mode. Keep the histogram visably all the time.
3. Use the sample tool and click on the unexposed area (11x11 sample are is fine).
4. Create a new layer and fill it with the sampled color.
5. Invert the new layer and set blending mode to "Color dodge". Your mask should be gone now.
6. Use crop tool to cut away all unexposed film. Don't flatten.
7. Create new curve layer and choose negative from presets meny. Then set a few anchor points to shape a C cure (or inverse C curve depening on you settings in the curves tool). This part is artistic - but typically a steep curve in the highlights that flatten out in the shadows give you nice highlight separation and good contrast. The number of anchor points needed depends on scene, inital exposure and artistic preference - sometimes one point is enough but 3 or 4 is often needed. But keep the curve smooth, no "bumps".
8. Create a new curve layer and drag the far left and far right points inwards to fill upp the histogram. Your image could look heavely posterized by now, but no worries - that is because preview in PS is only 8 bit but the underlying data is 15-bit (not 16, we work in Photoshop) and that is enough to give smooth transistions.
9. Create a new curve layer and use the grey sampler to color balance - this is an artistic choise but I try make is as neutral as I can and leave the fine tuning to later.
10. Flatten image - now you should have a very good starting point to work with in Photoshop, Lightroom, CameraRaw or whatever you prefer.
One example with good highlight separation (at least to my eye):