Core rules might be enough depending on how the DM wants to work the possession.
Dispel Evil
Abjuration [Good]
Level: Clr 5, Good 5, Pal 4
Components: V, S, DF
Casting Time: 1 standard action
Range: Touch
Target or Targets: You and a touched evil creature from another plane; or you and an enchantment or evil spell on a touched creature or object
Duration: 1 round/level or until discharged, whichever comes first
Saving Throw: See text
Spell Resistance: See text
Shimmering, white, holy energy surrounds you. This power has three effects.
First, you gain a +4 deflection bonus to AC against attacks by evil creatures.
Second, on making a successful melee touch attack against an evil creature from another plane, you can choose to drive that creature back to its home plane. The creature can negate the effects with a successful Will save (spell resistance applies). This use discharges and ends the spell.
Third, with a touch you can automatically dispel any one enchantment spell cast by an evil creature or any one evil spell. Exception: Spells that can’t be dispelled by dispel magic also can’t be dispelled by dispel evil. Saving throws and spell resistance do not apply to this effect. This use discharges and ends the spell.
Dismissal
Abjuration
Level: Clr 4, Sor/Wiz 5
Components: V, S, DF
Casting Time: 1 standard action
Range: Close (25 ft. + 5 ft./2 levels)
Target: One extraplanar creature
Duration: Instantaneous
Saving Throw: Will negates; see text
Spell Resistance: Yes
This spell forces an extraplanar creature back to its proper plane if it fails a special Will save (DC = spell’s save DC - creature’s HD + your caster level). If the spell is successful, the creature is instantly whisked away, but there is a 20% chance of actually sending the subject to a plane other than its own.
Banishment
Abjuration
Level: Clr 6, Sor/Wiz 7
Components: V, S, F
Casting Time: 1 standard action
Range: Close (25 ft. + 5 ft./2 levels)
Targets: One or more extraplanar creatures, no two of which can be more than 30 ft. apart
Duration: Instantaneous
Saving Throw: Will negates
Spell Resistance: Yes
A banishment spell is a more powerful version of the dismissal spell. It enables you to force extraplanar creatures out of your home plane. As many as 2 Hit Dice of creatures per caster level can be banished.
You can improve the spell’s chance of success by presenting at least one object or substance that the target hates, fears, or otherwise opposes. For each such object or substance, you gain a +1 bonus on your caster level check to overcome the target’s spell resistance (if any), the saving throw DC increases by 2.
Certain rare items might work twice as well as a normal item for the purpose of the bonuses (each providing a +2 bonus on the caster level check against spell resistance and increasing the save DC by 4).
Arcane Focus
Any item that is distasteful to the subject (optional, see above).