I give you, the commoner.
d4 hit points.
Wizard base attack bonus (1/2 level)
Poor saves (all). No class features.
I'd bump em to 4+int or even 6+int skills/level though. After all, it's all they have. Give them improved skill use (all) and.. .hmm... what else could they get enhancement wise?
No multiclassing allowed, and therefore no LRing into it to gain the past life.
Make it work! I'm thinking a quarterstaff THer, since it's a simple weapon (which technically they only get one of...). Probably half-elf with the cleric diletante. Gotta make yourself useful somehow, though you could Cross Class UMD I suppose.
Obviously, would never be implemented anyhow. The past life passive would have to be insanely good for anyone to want to do this!