It's a Summon spell. Conjuration (Creation) level 9. Duration is 1 round/level.
Creature type is Elemental, uses appropriate stats/BAB for a creature of it's Hit Die.
Creatures who strike the thing in melee must make a fortitude save or take 5d6 Magical Damage. You know...for hitting a Sphere of Annihilation..
The only attack it actually makes is to cast Disintegrate 1/round, making a ranged touch attack, at a caster level equal to it's Hit Die.
Spell Focus/Greater Spell Focus/Epic Spell Focus/Red Wizard Specialization (Conjuration) all add an additional Hit Die to the creature, just as it would a summoned creature. This increases the Attack Roll/Caster Level of the creature as appropriate.
The only issue would be, somehow, to be able to make the creature use the Caster's DCs. I don't know if that can done in scripting, but it might be worth a try?
Thoughts? Witticisms? Comments?