Hoggins

Well, keep in mind that using a weapon inappropriately sized takes a -2 penalty on attack rolls.

As far as feats, I can't think of any that allow you to dual-wield rapiers as though they were both light weapons. But, I'll tell you what, if you take Weapon Finesse, Weapon Focus (rapier), and Two-Weapon fighting, I will work on a feat that allows you to use two rapiers.