1) Spellstiching.
In Complete Arcane on page 162. Add this template to an undead with a Wis score of at least 17, and make Extract Gift one of its granted SLA’s.
Pro: It does not require any particular build to function, thus no character level investment. Only 1,000gp and the Craft Wondrous Item Feat.
Con: Requires 500XP for each point of the creatures Wis score, thus a minimum of 8,500xp. Caster level is based on HD. Caster level difficult is to raise. Only usable 1 or 2 times per day. Resigned to dealing with undead.
2) Guardian.
In the Monster Manual 2 on page 182, and in the update on page 10. The Runic Guardian can be give a small number of SLA’s, make Extract Gift one of its SLA’s.
Pro: Costs less XP than Spellstiching. Not restricted to dealing with undead, thus not evil. Only character investment is Craft Construct.
Con: Costs a lot more GP than spellstiching (note, price was lowered in the update). Caster level may be based on either the guardians HD or the creators caster level, ask your DM. Caster level difficult is to raise. Only usable 1 time per day.
3) Dweomerkeeper.
In the Web Enhancement for Complete Divine. Can cast her spells a certain number of times per day as though they were Supernatural Abilities. Requires you use Limited Wish, Wish or Miracle to emulate Extract Gift, due to the casting time restriction.
Pro: Uses your caster level, thus it is easy to raise it. Doesn’t require any created minions.
Con: Using this method, you are roped into playing this PRC.
4) Shadowcraft Mage
I will not detail it all out here, but it is possible for this PRC out of Races of Stone to be able to cast free Miracles out of 8th level spell slots.
Pro: Uses your caster level, thus it is easy to raise it. Doesn’t require any created minions. Caster level starts out higher that the Dweomerkeepers due to Earth Spell.
Con: Using this method, you are roped into playing this PRC. Requires 1-2 more levels than the Dweomerkeeper using Limited Wish. Requires many specific feats to make this work.
There are other methods, but it all boils down to this. You make a pet that can do it, and it can’t do it well, or you play a build that can do it, and you’re stuck with that build. Of course, there are worse builds to play than Dweomerkeeper or Shadowcraft Mage.