More Heroes of Horror taint tricks. In this special episode, a stupid early entry trick!
So, the HoH feat Eldritch Corruption gives you, among other benefits, sudden heighten (two levels up) 3/day, which costs you or an ally four points of con damage each time. It requires another metamagic, and moderate depravity. Moderate depravity is a cinch with the undead type - you just need to have more charisma than wisdom.
So, let's see what we can do with this.
Necropolitan Human (Druid 2)
Feats
Human: Magical Training (cast 2 cantrips, gain arcane CL 1)
First level: Precocious apprentice (cast a single second level spell)
Flaw: Some metamagic of your choice
Flaw2: Open slot
Necropolitan Taint Feat (free with every purchase of moderate taint): Eldritch corruption
What does all that get you? The ability to cast a single fourth level arcane spell, that's what. Your animal companion is a squishy source of sacrificial constitution, so keep it safe. There's no range limit to the feat, so if you can keep it locked up and strapped onto a Bed of Lesser Restoration (stronghold builder's guidebook), why not?
Or you could get some chickens, feed them, and succeed on a handle animal check to make them like you. Then, when they least expect it (and have no idea what's going on), rip their life force out to power your spells. Keep a portable hole full of them, and never look back.