Short of feat chains and expensive items, what methods exist to buff up the caster-level of that scroll you're holding in your hands right now and would like to squeeze one extra CL's worth of rich, creamy goodness out of?
Hard. I mean the cyphermage prestige class does this and more, but the cost is higher still.
Augment summoning works with SLAs because it names spells I think. Any boost which names spells might arguably work; boosts which don't and just apply to spells are harder to make the case for. Spell specialization if it matches, but maybe not a ley line guardian's +1d4-1 to CL.