MasterOfHeaven said:Grrrr! This is about the fifth time I've tried to post this... hope it works.
The buffing spells mentioned above are good ideas, and you should use them. However, he does have Rogue levels, and he should use that to his advantage. Give him the Blind Fighting feat. Cast a few buffing spells before they show up, and then cast Silence on his shield/weapon. Then, when they show up, cast Deeper Darkness on his shield/weapon. Free sneak attacks, and they can't see or hear you. If you want to be nasty, cast Summon Monster IV and summon 1d3 Fiendish Dire Bats before you cast the Silence spell. Have fun.
Unfortunately, anything that gives a miss chance, such as the concealment from darkness, negates sneak attacks. The darkness plus bats is a good option, though.
As for the ambush, I think it's hard to go wrong with the setup you have. Just make sure that he has his buff spells prepared (magic vestment, greater magic weapon, circle vs. good, shield of faith, divine favor) beforehand. Once that's in place, try to sculpt the ambush to reflect his faith. He could summon creatures to try to set up flanking situations. He might try to kill divine spellcasters first, then use poison and contagion on arcane spellcasters or rogues, and then flee to let his spells work their magic, so to speak.