I like dweomerkeeper or unseen seer personally. Although both of those are likely to lose at least 1 caster level in prereqs.
Unseen Seer progresses divine casting? Hmm... that would be nice... (Edit: It progresses arcane only. I'll probably just go with Shadowcrafter, or maybe dip into Mystic Wanderer for a familiar.
)
And while we're on the topic... I just had a realization about one way that a SCM is even better than a "normal" mage at BFC (above the huge amount of flexibility they have, and focus on a single spell, etc). As long as your % reality isn't jacked up to obscene levels, your allies can likely ignore your (low level) spell effects. So that
shadow Web spell that you tie the enemies up in? Your allies only have a 30% chance of suffering from the cover that it grants when hitting them with missile fire. And they have an 80% chance of ignoring your
shadow Grease spell, even if they get caught in the area and fail the Reflex save. And against a lot of enemies, this still may not clue them in that your spell is in fact an Illusion.