You have to go full out renegade.
So no upgrade + worst character selections + renegade + renegade options (i.e. keep the human reaper) + as little paragon option as possible during gameplay = dead shepard?
and don't heal your scars yeah pretty much.
That didn't work.
I have a full renegade no-repair save (as well as not healing the scars; I like it when it was glowing red =P), and Shepard still survived.
Everyone died 'cept the new dude (from the DLC; w/e his name is) and Joker, but I (Shepard) still survived.
ARG... WHY WON'T YOU DIE.