Well, your best bet is to use Arcane Explosion with the Arcane Subtlety, Arcane Concentration, and Arcane Impact talents maxed out. After that I recommend fire for Blastwave, Dragons Breath, and Master of Elements. But keep in mind what Sushi said above, you will pull the mobs off the pally by your 3rd cas (maybe 4th with arcane subtlety), unless you wait 10 sec each pull for the pally to build agro. Honest all the pally will be useful for will be gather the mobs into a neat little clump for you, then it won't be much different than soloing them except you getting half the experience.
You didn't mention what levels you were referring to but I will assume it is new chars from 1-70. If that is the case I would just like to mention, in case you were under this impression, that AoE grinding is not the fastest way to level. In fact since they raised the quest exp rewards it is much slower and with a partner you can double that time.
I would recommend the pally be Ret at least from 1-63, and the two of you just DPS ur way thru the levels, it will be much faster and a play style where you can support each other better.
EDIT: If your really set on an AoE fest, would the pally consider going holy? Use the pally just to gather up the mobs but not fight to maintain threat. Once clumped up you pull them off him with AoE and he can add more with his Consecration, heals, and taking care of mobs that get outside your AoE radius. If you go this route Frost and imp blizzard instead of fire would be a solid tactic (just don't get frost bite if you use Blizzard). Sorry this post turned into a "what the Pally should do" rather than focusing on you. I just think you will find that your carrying a Prot Pally way more than if he was a different spec. And that is just due to the difference in killing speeds of the play styles.
Edited, Aug 29th 2008 12:47pm by ocyen