Extract Gift is a spell from Fiendish Codex I that allows you to take power from a demon and gain it yourself. But there are some problems involved:
1. Casting Time 1 hour. You need either a willing, sleeping or trapped demon.
Solution: Planar Binding is just what we need for this. For Planar Binding, you need a Magic Circle. And Dimensional Anchor on the Circle (for 24h duration).
2. Spell Resistance still applies. So be careful what demon you summon. Assay Spell Resistance (SpC) should help you for +10 on the checks. (but I'm not quite sure this works with the duration?)
3. The demon may try a Charisma check vs. 15+1/2 CL+your Cha. Useful ways to max the odds here?
4. You may try to convince the demon, that he should grant you some parts of his power. This is an opposed Charisma-check, again, we need some ways to max our check here. Or to minimize his. Some kind of reward may grant a bonus to our check (adjusted by the DM) of +0 to +6. Check out 5. for this.
5. If your demon is not willing, he will get his will save. Granting the demon some kind of power increases the DC by +1 to +7. But I'm not sure you want a demon to gain some sort of power (like looking through your eyes), because if he gets mad at you for some reason, it gets very easy for him to find you.
Solution: Just grant him the ability to be bond with you telepathically for +5 DC and kill him afterwards.
6. You need a high CL for a high bonus. Some ways to increase the CL via spells or items? (should be as cheap as possible)
-Mystic Surge (PHB2 spell) grants an allied caster +1 CL and +2 DC for 1 round, can this help anyhow?
7. You need Material and XP components, if the spell fails, you still pay them, so make sure you get a chance of success of at least over 95%.
Of course, you have to be careful what demon you summon, so he fulfills the requirements but has low SR, Charisma and Will save.
Do you have some advice for me to optimize the use of this spell? (without cheese, class levels or feats, also I don't have leadership but I got party members that could help)