Three fuzzy useless ideas:
The backlight is supposed to be the hottest light on a portrait. If that's the case, it might be possible to use a manipulation tool like Photoshop Curves to create a picture those extreme highlights are slightly green, thus cancelling out the purple. That would be a custom gamma tool.
There are tools that can be made to recognize one color and put another color in its place. In Photoshop, it's called "Repace Color."
This may look funny, but set up a chroma key and use that purple as the key color. That will create a "hole" where the purple is. use the same video but in black and white as the third key signal. The upshot is a picture with black and white highlights instead of purple. Might work.
Koz