Hrm, I could have sworn I replied to this already...
Anyhoo, I'd ask the DM if we could refluff Rainbow Servant to be non-good then take Dread Necromancer20, Rainbow Servant 10//whatever on the other side
This would give you the lich template, CHA based casting, oh ya and all cleric spells spontaneously on your list, no more worrying about which spells to pick
For the 'other side' you still have all kinds of room for shenanigans like Black Ethergaunt, Fiend of Possession(and it's insane prerequisites), or the social murderer that soro mentioned earlier
Edit: redacted binder recommendation after re-reading the op, dang
Edit: ahem, can a thrall be gestalt?
