In my endless pondering over character ideas I find myself coming up short with a good wrap up for a character I've been thinking about. The character in question will be a focused specialist Conjurer (ban Evocation, Necromancy and Enchantment) who bargained to become a Warlock and then went into the Eldritch Theurge class. I would plan to take three levels of Wizard, three of Warlock and the full ten of Theurge. Now the question is what to take for the final four levels? If possible I would like to advance both base classes' spellcasting power, but I am not adverse to sacrifices spells for something else.

The role playing idea for the character has him at Lawful Evil. For race I'm inclined towards Illumian with the Naenkrau sigil. I'm willing to substitute the race or alignment for something else though.

Mechanically I am going for a guy who uses his invocations mostly for all-day buffs while using his spells for battlefield control and calling in back-up.

No third party books, but Dragon is ok. No cheese.