Boosting the caster level of a long casting time spell using spells

[Zorgoth]

I'm wondering if there's any way to use something like Spell Enhancer or Quickened True Casting to boost the power of a spell like Create Magic Tattoo or Planar Binding.

As far as I can tell from the Spell Descriptions section, swift action and quickened spells can be cast while casting another spell, since that takes a full-round action each round.

There's four ways to think about it, as far as I can see:

1. You can cast a booster spell right before you start the main spell, and the main spell will be boosted (I think not).
2. You can cast a booster spell as the main spell is finishing, and the main spell will be boosted (more plausible. the casting time description says that you determine the precise effects of the spell on the round that it is cast, but the impact of this is not clear here. The pertinent question is whether you can count the main spell as being cast "this round" on the round that it finishes casting.)
3. You can cast a booster spell repeatedly during the casting time of the main spell, and if it is active for the full duration, you win (difficult, but plausible if using rapid spell and possibly extended boosting spells)
4. You can't benefit from these booster spells at all.

What do the wise folk of this forum think?