Here's what I would suggest...
IMPROVED AID ANOTHER
Benefit: When you use the Aid Another action in combat, you can make your attack roll against AC 15 to give a +4 bonus on your ally's attack roll or armor class.
Normal: When you use the Aid Another action in combat, you make an attack roll against AC 10. If you succeed, your ally gains either a +2 bonus on his next attack roll against an opponent that both you and your ally are adjacent to or a +2 bonus to AC against that opponent’s next attack (your choice), as long as that attack comes before the beginning of your next turn.
GREATER AID ANOTHER
Prerequisite: Improved Aid Another, BAB +6 or more.
Benefit: When you use the Aid Another action, it is a Move Action, rather than a Standard Action.
SUPERIOR AID ANOTHER
Prerequisite: Greater Aid Another.
Benefit: When you use the Aid Another action, you can grant the bonus to one additional ally that is adjacent to both you and the chosen opponent.
PERFECT AID ANOTHER
Prerequisite: Superior Aid Another.
Benefit: You can use the Aid Another action to grant a bonus to an ally as long as both he and the chosen opponent are within a number of feet equal to five plus five times your Intelligence Modifier (minimum 1). For instance, with an Intelligence score of 10, you could use the Aid Another action to grant a bonus to an ally if both he and his chosen opponent were within 10 feet of you.
Normal: You can only use the Aid Another action to grant a bonus to an ally so long as you and your ally are adjacent to the same opponent.
Later
silver
Since I like feat chains so much, I've editted in a couple more feats into this chain.