wowza, alright- this reminds me of the idea me and BoD had a while ago, an insane gnome demigod, who was charged with opening the unopenable door, and he always sits there and picks the lock... Really cool, but if yer looking for an awesome rogue build you've come to the right place, I LOVE ROGUES, bards, and arcane casters!!!
i think rouge/dungeon delver would suit you well for a full trap disarmer.... You want to max out disarm device, and search, and listen, and probably spot, and don't forget hide/move silently, so he could sneak by the PC's. You should invest in boots of striding and springing to bring his speed up to par, and he should wield an elven weapon, howabout Elven thinblade, from complete warrior, expensive, but its a one-handed weapon that deals 1d8 damage with a 18-20 crit. and its elven.
You should get MW thieves tools, Expandable pole, grapple firing crossbow, longrreach tongs, MW longspoon thieves tools, and a type IV mechanical burglar. You should get him a rope, and whatever else you deem nececery. Those were just the basic thieves kit for thieves who like to stay alive...