It's mainly items and a spell or two but it should give you a decent bonus.
Moment of Prescience - Your caster level as an insight bonus to checks such as these. It is an 8th level spell though.
Circlet of Persuasion - +3 bonus.
Cloak of Charisma - +2, +4 or +6 bonus to Charisma,
You should be able to net yourself at least an additional +10, or at the very least +5, using those things.
What class are you entering in with? I'm assuming Wizard, but are you using any variants and such?
Edit: Partially ninja'd