Circle Magic Without Red Mage?

[Deth Muncher]

Hey everyone. I've been trying to wrack my brain (and my archives) for this, and I can't seem to find an answer. I could SWEAR there's a way for casters in 3.5 to take a feat to allow casters to cast in concert in order to up the caster level of a spell. However, try as I might, I can only find the Red Mage class feature about it, as well as the "Craft Tattoo" feat, which is reserved specifically for Red Mages and their own casting.

Does anyone know what I'm trying to find, or did my mind just make it up?

[Alleran]

Off the top of my head, you can also use Halruaan Elder or Hathran for Circle Magic. I don't know about any feat.

[Kelb_Panthera]

If I'm not mistaken, the hathran from FRCS can do circle magic too. I'm also pretty sure Ghostwalk has a feat that lets you perform circle magic. Those are the only other two I can think of in WotC sources.

[AntiTrust]

Cooperative Spell from Carc does what you're wanting I think