When reading the Mortal Conviction keystone, I realized that it was worded in such a way that all non-banner, non-mine auras had their reservations removed, but you were only limited to one non-banner aura with no duration. The unique boots March of the Legion allows you to cast auras as temporary, 12 second buffs through a built-in support gem called Blessing, but Blessing still reserves the aura's mana cost for .2 seconds. Increased skill effect duration (or self-curse temp chains) can extend the duration of the temporary auras.
So I did some testing with a March of Legion and a Malachi's Simula for Mortal Conviction, and you can get up to five auras without any life reservation (one free from Mortal Conviction, four socketed in the March of the Legion). There is a bug, however, where your permanent aura switches off every time you cast an aura with Blessing--you can recast it without a problem, but you have to reactivate it every time you cast a temporary aura.
Mortal Conviction doesn't prevent you from using Heralds, Banners, or Summon Skitterbots (or mine skills generally) to reserve your life, and fortunately these reservations are permanent and don't get switched whenever you cast an aura with Blessing. (I didn't specifically test Arctic Armour, Midnight Bargain, or Blood and Sand, but they should also work, as they aren't auras.) The Blood Magic + Mortal Conviction keystones don't have the mana multiplier associated with a Blood Magic support gem, so you can go low-life with a bunch of non-aura spells.
Tl; dr: Without any investment of passive points into auras, a low-life build using Blood Magic and Mortal Conviction can have five free temporary auras with March of the Legion plus three heralds and a banner (or two extra spectres, a herald, and a banner).
