Stay at range. Figure out how to work Far Shot and/or a Distance bow into the mix.
If he has, say, a +1 composite longbow with the distance power, he has a range increment of 220 ft. (Adding Far Shot would generate a range increment of 275 ft.) Fireball at 7th level only has a range of 680 ft. Plus figure that the wizard can move another 30 ft. before casting, for a total of 710 ft. So, your guy stands 800 feet off and fires away. He's -6 to hit, but basically untouchable. At 7th level, with a Dex of 20 (elf, include +2 gloves if you like, or a cat's grace potion) and that +1 bow, he starts at +13 to hit, so after accounting for Rapid Shot he'll be at +5/+5/+0 for a full attack. You could tweak it to be higher (bigger dex, better bow, weapon focus), but that's pretty good.
The build I'd use off the top of my head (28 Point Buy so the Dex is a little lower, and I fudged a little on NPC gear value - obviously it changes if you use different starting parameters):
High Elven Ranger 2/Fighter 4/Deepwood Sniper 1
Str 14; Dex 18; Con 12; Int 10; Wis 12; Cha 10
Skills: Hide (+7), Move Silently (+7), Spot (+13), Survival (+11), Ride (+16), Handle Animal (+10), Listen (+7)
Feats: Track, Rapid Shot, Endurance, Mounted Combat, Mounted Archery, Point Blank Shot, Far Shot, Weapon Focus (Longbow), Precise Shot, Weapon Specialization (Longbow)
Abilities: Favored Enemy (Human) +2, Wild Empathy, Keen Arrows, Range Increment Bonus
AC: 18; hp 49; Init +4; BAB +7/+2; Fort +9, Ref +11, Will +3 (+5 vs. enchantments).
Gear: +1 composite longbow of distance (+2 strength modifier - Range Increment 300 ft. with mods, 1d8+5, 19-20/x3), arrows (lots), MW chain shirt (armor check penalty already factored into skills), light war horse, military saddle, signal horn, MW longsword, oil of magic weapon (x2), wand of CLW (1st caster level, 30 charges left), heavy wooden shield (not normally used, not factored into AC), potion of cat's grace (x2)*, wand of entangle (1st CL, 15 charges left), +1 cloak of resistance, potion of protection from good (x3).
*These potions do not improve AC, because of the max dex on the armor.