I've decided to houserule that characters start with their Con score as physical hit points at 1st level to save them being mauled/trampled to death by domestic animals.
This represents the real "toughness" damage they can take.
Its not quite the +20 hp kicker at 1st level Hackmaster gives and to my mind makes already frail first level characters more survivable - most can now take a couple of good whacks. The appropriate HD is then gained at subsequent levels as "non physical" HPs.
Of course this means corporeal monsters have more hit points as well......
Floaty things like wraiths use their listed Int/Wis as a base then add the appropriate HD.
I think this may actually work without wrecking the mechanics too much......B-)