As far as offical feats go. You have Bouncing Spell and Contagious Spell. But they probably aren't what you have in mind. There is the 3rd party feat Chain Spell, which I think does what you're looking for.
Outside of that I'm not sure.
I've pretty much resolved myself to either Chain Spell or Words of Power for boost Select target word. They are close, but a little high in the level increase.