I once did all the legwork for an attorney who got around this concept by proving that the individual was overweight and had most likely been affected by being overweight, while a less overweight person would not have suffered injuries as great in the accident.
If the person isn't overweight, you can apply the same logic to them being a drinker, partier, womanizer.....workaholic, or whatever. The idea is to show that they LIKELY had undetected pre-existing [preventable] physical conditions (due to their habits) that contributed to the severity of the injury.
Is this underhanded, and potentially a heated topic in the courtroom? Maybe. But if it is before a jury, believe me it makes them think. Just be careful if the person is terribly sympathetic, it could backfire.