Caster level 12th
This poses an obvious problem for most characters in E6: as 6th-level characters, they’re 6 caster levels short of meeting this prerequisite. There are a few bonuses to caster level out there, but most are specific to particular spells or types of spells, or limited-usage, in ways that prevent them from meeting this requirement.1 Off the top of my head, only the orange ioun stone provides a sufficiently consistent and blanket bonus to caster level that should work for feat prerequisites. Artificers get a +2 bonus to caster level for the purposes of actually crafting items, but this doesn’t appear to carry over to meeting item-creation feats’ prerequisites.
So, is there any way to meet this requirement? Leaving out any infinite or arbitrary loops, manipulate form in its entirety, or anything that breaks 6 HD assumption inherent in E6 (e.g. becoming a lycanthrope as a 6th-level character to get more HD to work with Practiced Spellcaster or something), that is. This is obviously cheesy but I’m trying to avoid “extreme” cheese. Outside assistance is frowned upon, but is valid if it’s assistance from another valid E6 character—assistance from monsters and other creatures is out. And I would like to actually have the feat, not merely get around it somehow, though it’s acceptable if actually using it requires some kind of set-up or special conditions (as long as those can be maintained for 8 hours of crafting).
Otherwise, all Wizards of the Coast-published 3.5e material, as well as all Dragon and Dungeon 3.5e material, is acceptable.
Any combination of race and class is allowed, again so long as it’s legal under the usual E6 rules (I presume some kind of 6th-level spellcaster is best, but if not then that’s fine). Any number of bonus feats can be assumed, again as usual for E6 rules.