This question was asked some time ago but until now it has only an answer about traits so this might help others who have the same question.
There are magical pieces of equipment that increase the AC bonus granted through aid another:
Gloves of arcane striking: They require the user to have the arcane strike feat and for that an arcane caster level. "When the wearer uses the aid another action to improve an ally's Armor Class, the ally also adds the wearer's Arcane Strike damage bonus to his AC against the opponent"
Benevolent armor enchantment: "When the wearer of a suit of benevolent armor uses the aid another action to give an ally a bonus to AC against an opponent's next attack, he also adds the benevolent armor's enhancement bonus to the ally's AC."
Ring of tactical precision: anytime the wearer gives or receives a numeric bonus from a teamwork feat or the aid another action, that bonus increase by +1.
Then there is the variant channel ability strategy. While the question asks for non class abilities variant channeling can be used by more than one class and as such I chose to include it.
On the other hand strategy states granting your channeling bonus to the aided creature's roll which makes it unclear whether it is applicable to AC, which is, no roll.
A character who has the channel energy ability from a class other than cleric may use these variant channeling rules if the class's abilities are tied to serving a deity. For example, paladins can select alternative channeling abilities if they serve a deity, as can oracles with the Life mystery (as they serve many deities), but necromancer wizards cannot.