Without using psionics, is there a way to reduce the absolute lowball minimum caster level of a spell completion magic item or spell trigger magic item? Likewise, is there a way to brew a potion at a caster level lower than is needed to cast the spell the potion contains?
The benefit of the feat Metacreative (Psionics Handbook 27) says, in part, that
You can create psionic items (including psionic armors and weapons, psionic tattoos, dorjes, power stones, and universal items) as if your effective manifester level were one less than your actual level (minimum 1st level). You must still be of high enough level to manifest the power in question. You can choose to use or not use this feat on each new psionic item you create.
The feat's examples then go on to clarify that this means, for example, a psionic item with a minimum manifester level of 3 (like a dorje that stores a 2nd-level power) can be created by a creature possessing the feat at manifester level 2 if the creature has a manifester level of at least 3.
The prestige class crystalsinger expands on this idea, gaining—so far as I can tell—the unique class feature metacreative creation that's essentially a variant of the benefit of the feat Metacreative, but, instead of being able to create psionic items as if the crystalsinger were a manifester but one level lower than normal, the crystalsinger can ultimately create psionic items that are up to five levels lower than normal! (In all cases, there's a 1st-level manifester minimum.)
For example, a psion 9/crystalsinger 9 can create a dorje that stores a 4th-level power yet that has a manifester level of but 2. By comparison, when most creatures create a dorje that stores a 4th-level power, that power has a minimum manifester level of 7. (This vastly reduces the dorje's price: the former dorje's market price is 6,000 gp while the latter's is 21,000 gp! This also, of course, sometimes reduces the item's utility, but for many effects this isn't particularly important.)
I want to do the same thing that the crstalsinger does but I'd prefer doing so without using psionics and especially without using stinky, old unrevised dnd-3e Psionics Handbook-era material!
Note: I am aware that a magic item's Caster Level isn't a prerequisite for the magic item's creation. However a magic item's minimum caster level is typically equal to the minimum caster level needed to cast the highest-level spell among the item's prerequisite spells. I'm interested in reducing the minimum caster level needed to cast the highest-level prerequisite spell so that, for example, attuned gems, etched runes, potions, scepters, scrolls, staffs, wands, and so on that hold high-level spells can be created at lower-than-the-normal-minimum caster levels.