All through, when you think about it. Him using bows is actually a handicap.
One of the biggest stop points for spellcaster offense is the Rod of Absorption. However, he uses bows which are two-handed weapons and the Rod must be held in your hand to benefit from it. Think about that for a moment...
He claims that you don't need it in your hand and even if you do he can quickdraw it as a free action.
I can see Quickdraw honestly. Free Action I can haz draw does kind of require a DM to step in. But Quickdraw isn't Quick-Puts-It-Back-In, he'll have to spend the Move action to put it away (preventing his full-attack, no mic for belt of battle) or Free to drop it (in which case cannot quickdraw). So there again, either acts as a performance handicap or at one round defense for 50k a severe WBL handicap.
But I'd remind him of the text, it's quite direct with it's in hand statement. "Absorption requires no action on the part of the user if the rod is in hand at the time." Which only leaves rooom to argue what action is it if it's not. And the answer to that isn't free (that's same as no action) or swift/immediate (don't exist in core) but can only be default action for using a magic item (standard).
Now he says he can sovereign glue the Rod of Adsorption to his bow and it counts as being "in his hand."
The fact that he is even heading down this road of absurdity shows that he is going to lose badly... A Rod of Absorption isn't going to be nearly enough to save him... You should be able to use exactly the tactics outlined in Lycanthromancer's post and beat him soundly. You won't even be in danger at all during the fight.
I'd still go ahead and say you cast CoP a half a dozen times before the fight to find out exactly what his strategy is, what his magic items are, etc. Just for fun.
Edit: Oh yeah, another strategy he'll almost certainly be hopeless against:
0) Go first (contingency, etc)
1) Time Stop (maximized via a rod)
2) Shapechange (share spells) on your familiar, to turn it into a beholder.
3) Gate in some horrible beasts which he has no hope of being able to defeat, especially while stuck inside an antimagic area.
4) Hole up inside a Wall of Stone inside of a Prismatic Sphere or whatever, and wait.
5) Time Stop ends, your gated creatures grapple him and turn him into paste, while your familiar is hovering above him and aiming its antimagic eye at him.